A lot of heads of non-profits get very rich running non-profits. Especially since they're running on donations and grants. The goodwill is a non-profit, yet the CEO of Goodwill makes millions per year. The NFL is another non-profit organization (along with all the other major sports leagues). How many billions do they make?

If Blender were released today I'm sure it would do very well as a commercial app. Didn't it start out as a nurbs modeler? Most sane people hate working with nurbs, which is why you rarely ever see them being discussed or demonstrated (yes there are others who swear by them. But there are people who still insist Betamax was a better machine than VHS too). But it, and its developers, are doing very well as a non-profit, so there's really no reason to change it. Sounds to me like the best business model they've come up with.