Money definitely has something to do with it. I don't want to shell out any cash until I'm fairly sure of what I want to do with my game so I can make sure I get whatever program is best for me, but if I decided I wanted to do a ROM hack instead, I could just grab a ROM and some of the tools off Google and get started, with nothing lost but my time if it doesn't work out. Until there's a free RPG making program out there with a functional Pokemon starter kit, this kind of jumping in and experimenting isn't going to happen, which means development moves a lot slower than it might. (Or that's how it seems to me, anyway.)
I think someone on one of the other threads mentioned that there're more tools to aid in development for ROM hacking than there are for the kind of programs used in GD, too, but I have no idea how true that is.