I used to work on telephone switches. We had 31 million lines of code. I can't remember the entire details since it was over a decade ago, but I believe Bellcore required us to deploy fixes for 70% of all reported bugs within 30 days. We were a huge, fat-ass company with 5000 programmers working on the same project and managed this. 90 days is a lifetime to fix a security problem.
The point behind having a deadline before publicly disclosing is that if one person has discovered a security problem, then some other people probably have as well. It is fair enough to give vendors time before you make disclosure but if the vendor is moving too slowly -- for whatever reason -- you want to give the consumers a chance to implement their own security work around. Because if you don't they are vulnerable.
Giving Microsoft 90 days to fix an issue is fine. They can prioritize it anyway they want. If they think it is super urgent, they can almost certainly get a fix out. If they think it is not so urgent, then they don't have to make a fix -- but they know that the problem will be disclosed.
Nowhere in Google's documentation of this problem do I see a massive issue. Google gave MS 90 days. MS found a fix but there was another bug so they couldn't meet the window. Google released the information. Nowhere do I see MS requesting more time or any indication that anybody in the process thinks that anything went badly at all. It didn't meet the disclosure deadline. That's just the way it goes sometimes.