The reason is that PC is made out of standardized plug&play components that you can make generic OS image for.

Yep, given the history of consumer technology as a whole it is really more amazing that the standard PC became a thing more than it is that people put up with what phones are today.

We all really owe a lot of gratitude to Phoenix for reverse engineering the IBM BIOS back in the day, and going to court to fight the IBM copyright lawsuit that resulted, as well as Compaq and all of the other IBM compatible clones.