In a nutshell Selling PC's with linux is not commercially interesting. An example is my local PC shop which used to sell computers with linux pre-installed has stopped, reason being not profitable. No maintenance as Linux just works all the time no viruses etc..
Whereas a windows PC will go back to the shop every 6 months on average for an "overhaul'..
I mean look at Dell that used to sell such PC's They stopped now, but maybe that was a certain kind of pressure from we know who.....
I offer a free linux install to all my 20 odd Web site clients, I never hear from them apart from when there is a hardware failure..
My local server is running Debian for 10 years now never a glitch and its just a P4..
Its a long road.