[bluGill]

Anybody can write a good kernel for one single computer (not just CPU) in a couple years. What makes linux useful is the vast amount of different hardware combinations it supports, often with "black magic" because some hardware doesn't work unless you do something weird (commonly you have to wait some amount of time after the power comes on before using it). One computer is easy, adding support for a second that is even slightly different is more work. Linux works correctly on millions of combinations by now (most of those combinations have not been tested but they would work)