I have no inside knowledge, but just observing the business motivation. SfB is bad because Microsoft doesn’t want people to use it; they want everyone moving to Teams. They also know they have an existing installed base, mostly (probably) of large companies who have the capability of dedicating a full team of people to run it. They have already announced that SfB will no longer get updates and the on-prem software will be discontinued soon. MS is pretty much just waiting it out until all the holdouts just cave and switch to the could stuff.