Well, blame WoTC for all of this. There is probably even no one to work with there at this point. The whole team, that Larian cooperated with, is long gone now, which doesn't inspire confidence for future projects.
I think it's frankly far fetched that WotC is the reason. If anything I could see WotC being willing to write a blank cheque for Larian to do "w/e" for Baldur's Gate 4 given how well received 3 was. It's much more likely they just want to do something else instead and the split was amicable.
Within the context of Swen's speech at the Game Developer awards it is pretty clear that it's entirely the fault of WOTC/Hasbro.
Given how Hasbro has behaved this isn't surprising. Insisting the game be released before 4th quarter earnings, firing the team that Larian was working with, refusing to negotiate in good faith...no wonder Larian is fed up.
Hasbro is a highly corporate holding company that doesn't respect, or appreciate artistry even when It makes them 90 million dollars. They have a corporate cave-man spreadsheet mentality, focusing on numbers while failing to understand the synergistic value that comes from a holistic approach. They fail by pushing out garbage preferring to cannibalizing their work for a short term win over a long term windfall. I see it all the time - it's the hallmark of corporate mediocrity.
Fuck Hasbro. Larian will be fine, they are taking the hard path that can lead to greatness.