That doesn't mean they are "normal PCs".

Define what is a "normal PC" to you, then. Is it just specs?

Your PC is built on a standardized architecture, your mobile device is its own bespoke SoC and requires unique, and often proprietary, methods just to boot and discover components.

It's the reason you can use any amd64 ISO to boot Linux on your PC, but each individual embedded device needs its own special image that is custom to that board, and often a custom Linux fork.