I've got to give credit to Microsoft and Intel for making it easy to create a PC company. Intel produces a reference PC design, and a large number of chips. So, the design can get minor tweaks, for putting the design into manufacturing. So, you have to manufacture, sell, and provide warranty support for the PC. Today, manufacturing can be outsourced .....
I missed where Microsoft came in.
It was IBM who made it easy to create a PC company. When they introduced the PC they did not think it important enough (a passing fad, they preferred mainframes) to make most of the stuff themselves so they contracted it out. Intel and Microsoft were just two of those contractors. And IBM did not stop those contractors from selling the same stuff to third parties - other computer makers. So a cottage industry of PC clone makers sprang up using Intel chips and of course MSDos, among other things.
In fact Microsoft made things hard for those other PC makers - and still do - like charging silly prices and stopping them from pre-installing OS/2, Beos or Linux. Alan Sugar (of Amstrad) said of the price of Microsoft's software : "... as a computer manufacturer we are really a servant of Microsoft ... the bill of material content of our computers, the highest price ticket item in there, is the royalty we pay them [Microsoft] to put Windows in the box"