I don't know their reasoning. Looks like it's not in the eula anymore I looked. But, because of tax reasons I can't list with them right now.
And unless I can start producing quality 3d models, that people also want to get, there really is not much money in stock models. As things are right now, people do not like my models.
I think the only way to make it from freelance 3d models is to take jobs, directly with clients.