John Carmack confirmed what fidotron said in the Quakecon 2012 talk which I stumbled across in the comments here recently: https://www.youtube.com/watch?v=MG4QuTe8aUw : he talks about ID artists referring to light-map dinking as "painting with light" and generally being reluctant to give up direct control of final appearances.

Likely you're both right, and while it's harder to learn how to dink scenes and assets with ad-hoc rendering techniques than just use raytracing, an artist who has already mastered the black arts of tweaking everything just so is going to resent losing that control and having to let the physics take over.