This is what it comes down to. Nearly every office job pays for the Microsoft enterprise suite and office 365 subscriptions, before tacking on third party tools for monitoring and info. sec. for IT. I would gladly ditch Office 365 for Open Office and Debian, assuming all the higher ups would be willing to take such drastic measures to reduce expenses. I think most employees would balk at learning "an entire new system" regardless of how minor the differences actually are at this point.

I'll give 'em this: Microsoft's model creates very sticky revenue with high switching costs.

Yeah no argument there from me, just wanted to point out that it's not always a choice

Another reason is that you are virtually guaranteed to find any application you need that supports Windows.