Yeah, I just don't see games needing access to such kernel level items.
My own example: I have an xbox 360 dancemat, which is unusable with the official drivers (they map the arrows as axes, so treat left + right as nothing). So I have to use the open-source XBCD, which frankly I'd treat as more reputable and better code quality than most signed drivers. But since no-one's paying the $100+/year to sign it, it's not signed. And while I understand why Microsoft wants someone to have skin in the game before they issue a driver signing certificate, they really need to find a way to ensure that reputable, established open-source driver projects get signed if they want users to accept driver signing; I wouldn't even mind being stuck on an old "certified" version or something.
If they're providing online servers for you to play on with other people, under the condition that you aren't cheating and they are responsible for stopping cheating for everyone, they very much do care and it is their business, if you want to use their servers.
Having custom drivers is how you get wallhacks or custom mouse control macros that eliminates some of the challenges imposed by the game (e.g. automatic recoil control).
For a single player game, I agree, who cares, but for online games that live and die by competitive play and stopping cheaters so people can enjoy it, there's only so many options of how to find cheaters and so much resources to put towards it, so you get stuff like this.