The Massachusetts Legislature had a hefty to-do list as it headed into the final days of formal sessions this week — and some of the items on it ultimately did get crossed off, including a $5 billion housing bond bill and other legislation addressing veterans’ benefits and parentage equality. But a multitude of high-profile, high-stakes bills didn’t get passed. Among them: legislation involving economic development, clean energy and the environment, overdose prevention centers, hospital oversight, pharmacy costs, maternal health and new liquor licenses for Boston.

Speaking with reporters after negotiations between the House and Senate had wound down, House Speaker Ron Mariano was asked if trying to hash out differences between the two chambers at the last minute, in the middle of the night, was a good way to make policy. “Why wouldn’t it be?” Mariano asked, adding: “People make mistakes in the middle of the afternoon.”

Senate leadership, too, suggested that the backloaded process wasn’t necessarily problematic. “We worked hard, we worked our best, we weren’t able to get it done at this time, “ Senate Ways and Means Chair Michael Rodrigues said, appearing with Senate President Karen Spilka and referring to the still-unpassed economic development bill.

Still, the unsuccessful attempt to hammer out agreement on a host of extremely complicated issues at the absolute last possible minute raises an obvious question: why wait so long to try to do so much?

The answer, according to many, starts with the fact that power in both the House and Senate has become increasingly concentrated in the hands of the leaders of those chambers and their most trusted lieutenants. For example, both the Senate and House recently ended term limits for the Senate President and House Speaker.

Jonathan Cohn, the political director of the group Progressive Massachusetts, argues that this dynamic creates a structural problem that naturally leads to a slowed-down pace.

“In any system … if you have too few people in charge of too many decisions, you get a bottleneck effect,” Cohn said. “And you have that with the Legislature, where you know that the decision making is ultimately Ron Mariano’s decision about what’s in the bill, Karen Spilka’s decision about what’s in the bill … If it’s all just coming through one person, that just slows everything down even more.”

But Cohn also believes there’s a tactical consideration at play. By finalizing key legislation at the last minute, he says — and packing individual bills with a sprawling array of provisions on a particular topic — the House and Senate pave the way for marathon negotiating sessions just prior to the session’s end, in which each side defers to its counterpart in some areas and has the favor returned in others.

This interpretation is backed by a legislator who asked to speak anonymously so they could be as candid as possible.

“They see this all as a horse trade,” the legislator said of legislative leaders. “They are negotiating various pieces: what the Senate puts forward, what the House puts forward … [Both chambers] have their own priority legislation that they individually really care about. And so they do these trades and negotiations, but one negotiation tactic is to stall and stall and stall, and that is something that gets employed. It’s like a game of chicken.”

This year, when it came down to the wire, neither side blinked on some key bills. Mariano said he was willing to spike his priority health care legislation instead of passing a watered-down version, and Sen. Michael Barrett, the Senate’s lead negotiator on the energy bill, said he’d rather come back to the issue next year than agree to a version that didn’t take consumer costs into consideration. 

Other tactical considerations may also be involved. Vick Mohanka, a former legislative staffer, is the director of the Massachusetts Sierra Club, which backed the sprawling clean energy and environmental bill that failed to pass before the formal session ended. He contends that, by introducing high-stakes bills as late as possible, legislative leaders make it harder for dissenting voices to push for change before House and Senate negotiators craft and pass a final, compromised version of the legislation in question.

“The smaller amount of time that they offer debate, the less they have to take into account what the people want,” Mohanka said. “You saw this with the Senate and House floor debates, where they would release a hundred-page bill, and they would say, ‘You have a couple hours, if you’re a rank and file legislator, to file amendments.’

“If you’re an advocate, you have to read the bill, you have to work with a legislator to file an amendment,” Mohanka added. “Let’s say there’s a really serious issue with the way a bill is worded: you only have a couple hour window to pick that up. And they know that, and they know it’s a way for them to escape accountability.”

There are other possible explanations worth considering. For one thing, procrastination is human nature for many of us, along with the accompanying rationalization that it facilitates creativity and sharp thinking.

What’s more, the working relationship between Mariano and Spilka has been strained for some time, and each seemed to point a finger of blame toward the other as the formal session drew to a close. If genuine animosity exists between two parties, it may not be all that surprising if they delay intensive engagement for as long as possible.

There’s also the question of electoral consequences, or the lack thereof. After the Legislature wrapped up its formal session with so many bills still unpassed, the Mass. GOP put out a statement attributing that outcome to Democratic dominance on Beacon Hill, where the party currently controls the House, Senate and governorship.

“When one-party rule devolves into the partisan, chaotic, inactive display that took place in the halls of Beacon Hill, it … points to the desperate need for more productive voices in state government, and that is exactly what the Republican candidates for State Representative and State Senate have to offer,” Mass. GOP chair Amy Carnevale said in a statement.

Carnevale has a vested interest in making that case: the Republican presence in the Legislature is currently so miniscule that it borders on the irrelevant, and the Mass. GOP is hoping to add seats in this fall’s legislative elections. But the idea that Democratic dominance and entrenched incumbency leads to ineffective lawmaking transcends partisanship.

“Almost to a person, they’ll just all be back in January,” Cohn, of Progressive Mass, said of state lawmakers. “A handful of retirements. Maybe somebody might lose a seat in a primary or general. But they’ll all be back. And there’s often a way in which they just see it as, ‘Well, we didn’t finish now. We’ll come back in a few months and maybe we’ll pass it then.’ … It flattens the sense of time, because if it happens now, if it happens next year, it’s all the same.”

It’s possible, of course, that negative attention currently being given to this year’s array of unfinished business could change that dynamic. In addition to the Mass. GOP, progressive Democrats seeking to join the Legislature are calling out what happened this week — like state Rep. candidate Bill Humphrey of Newton, who posted on X: “Passing no bills for a year and a half and then saying you ran out of time to pass bills at the last second is an astonishing way of governing.”

It’s an open question, though, how many people are paying close attention and care enough to actually try to change an entrenched way of doing business on Beacon Hill. And for now, the message coming from legislative leaders is clear: it may not be perfect, but the system works pretty well.

Asked why so much legislative business gets left until the last minute, a spokesperson for Senate President Spilka provided this statement: “The Senate is proud to have delivered significant policy change this session — including billions of dollars in housing investment, free community college, historic investments in early education and child care, and bills to make our gun laws the strongest in the nation, bring much needed services to our veterans, and ensure equity in our parentage laws.”

Spilka’s spokesperson added: “We remain committed to continuing our policymaking through informal sessions, especially addressing economic development, healthcare, and climate change.”

Whether that actually happens could determine whether the events of this week have long-term consequences or not.

Katie Lannan contributed reporting for this story.