Microsoft more-or-less does the same thing with Windows in the personal consumer market. With Office being online these days, the primary motivation for a lot of people to buy a Windows license for a computer instead of using Linux or buying a Mac is gaming, along with pure inertia.
This will be a problem with everything until games are FLOSS.
I don't think games companies are against mods generally, many have steam workshop support built in. Nintendo as the big exception here ofc.
Cheating is ofc a huge problem for multiplayer games and can absolutely tank some genres. Very mixed feelings about the kernel level rootkit type spyware but there's no denying that games companies are paying big money to put them there for the players benefit.
But if this became a common practice I think people absolutely would. Tons of professional quality games instantly available for free is such an incredibly good value.