It's not advantageous for a parasite to immediately kill it's host. By 'wiped out' I don't mean the literal death of windows installs, I mean in the sense that

It's not advantageous for a parasite to immediately kill it's host. By 'wiped out' I don't mean the literal death of windows installs, I mean in the sense that a pristine windows install will, on average, slowly accumulate cruft until it's on the verge of being unusable. It's not a 1:1 analogy. In a strictly practical sense, an individual windows install may not be nonoperational due to mal/spy/crapware, but the quality of the user experience goes way down as a result of it.