Whether it's because of a stigma attached to the idea or because recruiting an audience and organizing an event for them is a lot of work they're not interested in doing, I can confirm that most of the gaming creators I contacted with Otherworlds were willing to do pro-GM gigs when asked, but aren't willing to actively pursue setting them up for themselves.
I do not believe there is any stigma, as such, but a short time perusing these boards reveal that people play D&D with many different values of what they consider fun and the same applies to other rpgs. Running a rpg is a fair bit of work, even if you are just running a published module. It is not fun if you and your players are not on the same page. Now, imagine doing it for money.
Also consider, what happens in the event of a rules dispute?