Meh. it's not just that.
it's the fact the media attention doesn't merit his performances and because his style is so unorthodox as a QB. It also challenges widely held beliefs about what is and what isn't successful in the NFL. Football Purists hate "gimmicks" and enjoy seeing things like Wildcat and read option eventually fail in the NFL.
The media attention really isn't fault, but i understand people wanting tebowmania to end. The only way it ends is if he is not successful, hence you have people rooting against him.
In terms of what it takes to be a successful QB, he needs to learn how to pass better (which he has improved) in order to be a legit QB.