Demon hunter is a lot of fun to play. It's still the least played class in the game. It has the two races that are wildly popular but not many people bother because of the racial restrictions. Now introduce Tinker with only the little and wildly UNpopular races capable of rolling the class. There is not only the restriction that players hate but ALSO they'd be forced to play a race they dislike. Those two factors would destroy the class' chance of being any semblance of popular.