Because user-friendly means that even a tech-noob can easily set it up and use it right away without much researching.
If an OS requires ANY AMOUNT of command line, you have lost about half the population.
If an OS asks any remotely difficult question with techno lingo, you have lost an other quarter.
If an OS doesn’t work out of the box the way it should (like all their hardware functioning including audio), you have lost all the other not technology inclined people.
Windows is setup that it requires none of that. It may do something that you find horrific, but most people do not care as long as it works.