If I'm not mistaken, there was a lot of talk that Cassidy was let go by the Bruins because certain players didn't like him. Bergeron being one notable.
At the conclusion of their handshake line when they were eliminated in 2022, players started embracing Bergeron like it was his last game ever.
He wound up coming back for one more year, but only after Cassidy was let go. I think it was a case of certain players with a lot of pull not liking him. Same thing seemed to have happened with Tortorella in 2013 when he was fired by the Rangers. I remember there were people claiming it was Lundqvist who personally got him fired, but I'm not sure it was only him.
He’s not a known to be a players coach, and maybe there were some disgruntled players, but Boston was never going to keep Cassidy long term.
Cassidy had a year left at reportedly ~3m and then got a 5 year/5.5m in a no income tax state.
The Bruins don’t like big money or lengthy coach’s contracts because they like flexibility (aka being comfortable with firing their asses).
Cassidy had two 3 year deals: 17/18 to 19/20 then 20/21 to 22/23.
The Bruins could’ve kept Cassidy for a year but teams don’t typically have lame duck coaches without an extension. (The Canes did it with Rod but they’re weird freaks.)
The Bruins had even “started contract talks” with Montgomery in September but I guess those ended lol.
Montgomery reportedly got ~2m in his 3 year deal.