I imagine the DRM is contracted out to a company which the publisher uses for more of their games. The DRM guy or gal comes in a couple days around the end of development, imports some libraries, and sprinkles some function calls here and there. There either isn't the knowledge/time/co-operation to optimize it, or the actual devs are told to stay well away from the DRM stuff to avoid messing something up and causing piracy false positives.

Not that I'm in the know, but it seems likely that publishers can get code into the binary one way or the other.