Because more often than not, the new GM wants to bring his own people in, especially in this case, where the aforementioned disconnect was toxic.
I think the difference, at least I hope the difference this time around, is that everyone in the organization realizes that this is now a total rebuild. That this wasn't like before last year, when all of the unexpected retirements were considered the catalyst for the poor record the year before. This is a complete do over, and in that case, the new coach will have to be given the time to put his stamp on the team.
Of course, if they had asked me last january, I would have been happy to tell them that they needed to blow all of this up and start over. But of course, they didn't ask