The fact that consumers use Windows is a nice side effect for keeping mind share and to get people familiar and preferring windows when they enter the workplace. That's it. It's an accidental userbase that exists to be exploited.
Microsoft's money comes from Azure & Office(365). If you're not spending millions on enterprise support/software assurance (or whatever they call it these days) contracts, you pretty much don't exist to them.
Microsoft's core product is minimizing operational risk, not the software itself. You can piece together your own stack using best of breed options, but you're going to pay double the price or more, and introduce a ton of friction and risk.
Some businesses (everyone outside of the SV tech echo chamber) "need" Microsoft because its risk mitigation, which is the highest technical feature a business can ask for. Backwards compatibility, EntraID is good, and the compliance/purview stack solves nearly all regulatory headaches OOTB.
OTOH yeah there's a bit of legacy entrenchment, both from Microsoft's monopolistic behavior but also because they were the only ones with an "IT In a box" solution for non-tech companies. Having a cohesive identity, security, and device management ecosystem that can scale to hundreds of thousands of endpoints with a few mouse clicks takes a lot of engineering effort that not many others were doing at the time.
They didn't run Windows because they liked Windows, they ran Windows because it was required by the software they needed to run.
How will MS PMs meet their quarterly targets without Windows phoning home every moment someone is using it? \s