Most regular folk use the tools that come with the computer. That means running Microsoft.
The question is whether they would choose something else if given the choice.
Probably not as better the devil you know. The alternative is scary to most.
Most probably won't. I think you're greatly overestimating the technical chops of the average PC user.
Exactly. Most office workers don't really have a choice. Someone in the corporate hierarchy decided to get the Office 365 subscription because that way everything would come bundled up together.