TIH didnt make money for these reasons (I think)
1. It was released when another HUGE Marvel blockbuster was still in theaters/fresh in ppls minds and people were seeing it for the umpteenth time instead of seeing the Hulk
2. Due to TIH being released to IM, the marketing suffered. I know first hand that some restaurants were still handing out IM toys instead of Hulk gear. TIH was very "under marketed"
3. The reviews although generally favorable were no where near as the universal praise for IM. People tried to compare the movie to IM. IMO TIH was worse than IM but still damn good
So in short, TIH was released at a bad time, just like Hellboy II. Thats why it suffered the most. It should have been released this year...I mean look at this year after Wolverine, Transformers 2, GI Joe there are no more superhero/comic book films coming out. I strongly think if TIH was released this year it would have done better critically and financially.
By the time WOM spread about Hulk; Wanted (An R rated movie for men), Wall-E (A Pixar movie), and Hancock (Will Smith), were in theaters.
And if they do make a sequel just have Norton write it