Money. I think 10.0 will be announced at Blizzconline with a release date of Nov-Dec 2022, because Blizz needs to get another expansion out and they make a significant portion of their profits with a new release and the sales immediately following that.
Whatever they need to drop to make it happen will be dropped.
They aren't getting good press. Another reason for this schedule is that I believe they need or want to start re-framing the conversation around WoW.
I agree with you on the excuses, which they are pretty good at for using to explain why they don't fix things.