He is very good at the following things:
- being born rich
- investing in a slam dunk future technology everyone on the planet knows we will need, eg money on the internet, electric cars, space ships
- taking risks in combining the above
That is about as far as his skillset runs. As we've seen from twitter, when he doesn't have an entire layer of his organisation set up to run interference in him, he quickly runs companies into the ground. He has had zero original ideas.
He's also a dangerous alt-right racist nutjob.
Why do you think they do? Logically think it through.
Market sharen and incumbent advantage. Ease of adoption (or appearance of). Ubiquity and lack of need to retain. Predatory behaviour by MS. Different priorities for users.
Unless you actually consider the real reasons why Windows is so widespread you'll never make a dent in it.