I think it's really just a combination of everything.
The whole Tim Tebow experience is a big distraction and while I'd imagine there are probably a lot of teams that would be willing to embrace (or simply tolerate) the hoopla surrounding him if he were an elite level QB, it is simply not worth the headache for a backup QB. It's sort of like Chad Johnson's tenure with the Bengals, most people were willing to tolerate his antics when he was one of the best WRs in the game but once his skills started to erode those antics grew tired and he was shown the door.