They can't. That's why I hate people using that chestnut in relation to Linux: It doesn't work for two reasons which stick out at me.
Reason one is because Linux is GPL'd, Microsoft can't extend Linux without giving its extensions back to the community.
Reason two is because Linux is already established in multiple realms, so Microsoft can't bully its way into dominance. Microsoft has a respectable presence in server rooms, but it isn't absolutely dominant by a long shot. Microsoft probably has something going on in the embedded/hobbyist SBC space, but there's no path for them to dominate there. And, FWIW, Linux owns the supercomputer world. I also can't see IBM falling over itself to put Windows on mainframes.
