Microsoft pretty much owns the de-facto standard for PC operating system, office applications, e-mail, calendar... And use that to extend itself beyond with services such as Office 365, SharePoint, PowerBI, etc.

I'd guess far more established companies go with hosted Microsoft apps than Google's.

Don't forget GitHub. Also a monopoly in PC gaming, in a duopoly in console gaming, in the process of buying Activision, also eyeing on practically buying OpenAI if not on paper.

I think OpenAI will realize Microsoft's intentions and counter them before Nadella even knows he wants it.

Which business isn't locked in to Word, PowerPoint and Excel? Why is Windows compatibility so important? What OS does virtually every desktop computer run? Microsoft has an almost total monopoly on these things.