Well, valve and AMD have worked together on this. Apart from that, steam is a DRM platform and there is a lot of tracking going on all the time (also during login) and in games. I don't know what the rights look like anymore, because there was a change at steam once, but steam itself should still have root/system rights somehow. In other words, it wouldn't be a problem that anti-cheat solutions could act outside of their prefix. Maybe valve is trying to get publishers to support them with a platform they can trust. (Of course i could be complete wrong)

Gameindustry. Good stuff against tracking.