John Carrier said:

The reason is similar to why Windows sells so well. It's "good enough"
for undiscerning use, and heavily marketed.

Certainly there are numerous flavors of Unix and Linux
available, but for average Joe/Jane that's not a realistic option.

In this case, "average" means 99% of the population.

really have to be a systems kind of person to get an alternative OS up and
running.

That's the nub. Similarly, mostly true music nuts (and equipment
geeks) are the buyers of systems costing over $20,000. I know several
well-to-do people who think nothing of plunking down $60K for a Lexus
or BMW but think of a home audio system as just another appliance. And
not because they don't spend time in their beautiful homes.