It's both easier and simpler

I think part of the problem for OEMs is that with a "typical commercial licensing agreement" they have a single, usually friendly, person to talk to (this is a slight simplification in some cases, but still). With a GPL product they may potentially have to deal with any of the people who contributed to it, without even being sure how many people that may be, and they certainly can't be sure that some of those won't be actively looking for ways to hurt them. Which usually won't be the case of course, but I think the risk is still worrying for them.