I think some are missing the point.
When the Bucks hired Griffin, it was before the Dame trade and the belief in upper management and Griffin himself was that the team was going to go through a rebuild of sorts, an experimental season. This is what sparked Giannis to become more vocal with odd comments questioning the integrity of the team, particularly ownership intentions, and making subtle remarks about leaving or doing what's best for himself.
Allegedly after that first-round defeat, the front office did not approach this season to win a championship season but to try and incorporate a new identity, etc however that all changed the moment they by luck acquired Dame just a few weeks before the preseason started.
They would've never hired Griffin in the first place if they knew they were acquiring Lillard. They would've gone after a veteran coach, unfortunately they couldn't fire him after getting the trade for Dame. So they waited, watched from a distance, and allowed him to prove himself but as others stated despite the team's 30-13 record the team's dynamics and overall vibes weren't clicking and management and even the players (Giannis, Bobby, etc) noticed what we as fans didn't see.
As some reports said it wasn't shocking to those close to the Bucks organization and locker room to see Griffin get fired, he was basically on the clock once Dame came to Milwaukee.