Actually, GoD made a loss on JJ2 due to bad advertising(I think I only saw 2 ads for it in my whole lifetime). Also JJ3 wasn't finished due to the same reason many promising games never get finished: these days, publishers dont like taking risks. Epic couldn't find a publisher, and thus had to cease the game's creation.

But if Midway(Epic's publisher I believe) sees potential in a new Jazz game, it's pretty much going to be made.