They hate each other
For me, the Bruins are having trouble for whatever reason executing plays on the ice this season. We don't know the reason for it, but they look nothing like the team they were last season. Adding to the fact that they added a "top 6C" and top 4D, they should be playing at least on par or better than what they have been showing.
We can debate Montgomery's results, but although his firing led to giving the Bruins a bump with Sacco becoming the head coach, his firing wasn't a direct correlation to the Bruins' performance this season as they are still struggling.
That leads to a few theories. Are multiple guys on the team playing through injuries, and the reason why the team is playing subpar may not necessarily be because of the injuries but because they know they may not have a chance this season due to the injuries needing attention in the offseason?
Are the Bruins a mentally fragile team? With the losses piling up, have they lost their confidence in themselves? Did their 1st game against Florida break them when they got walloped by the Panthers after making those two big additions in the offseason?
The third could be that there is a rift in the lockeroom. We can point to McAvoy early in the season saying how Brad's leadership is a bit old-fashioned with holding each other accountable. We can go back to February 2023 where this was published in the Globe:
None of us thought anything of it. Maybe because the losses are piling up, Pastrnak and McAvoy are annoyed of Marchand's "leadership," but I will say this, it hasn't been a problem before. Maybe because everyone is expected to get along with one another on the team that this is causing potential rifts in the room, but it's also noted that the 2011-2013 teams had different cliques in the lockeroom. They ended up just fine.
I think there would be more credence to the theory of Lindholm or Zadorov causing a rift in the room which would explain why the Bruins are playing so poorly compared to previous seasons.
It's wild for Keefe to say what he said without any backing to it because saying something untrue would absolute bomb his reputation, but he could also just be doing it for ratings so who knows. It's not like what he said wasn't said in 2023 already. Half-truths do sell though.