Their investment in OpenAI, giving them what was, at least ~1-2 year ago if not now, the best possible LLM to integrate in the office suite yet they are unable to deliver value with it.
Their ownership of Xbox and Windows should have allowed them to get a much better foothold in gaming yet their marketplace is still, to this very day, a broken experience with multiple account types. It's been 10 years.
The counter point is Azure obviously which still has great growth numbers, but that's a different org.
From the outside, it just seems like they should be doing better than they are. They have much better business integration than Google and Amazon. The fit is obvious and people are borderline hooked on excel. Why aren't they dominating completely?