I built my own rig and bought Windows directly from Microsoft, under no circumstance am I going to risk my security by rummaging around in shady places for something as critical as an operating system.

I’d also go out on a small limb and bet that most gaming rigs are at least partially OEM. I have the knowledge to put together my own gaming/dev workstation - but I’d rather just get a prebuilt that isn’t going to become a timesuck of crappy boot times then swap some components.