Why? All it would take is word of mouth to remedy that. At the end of the day Hulk's just not a franchise player.
A good word of mouth could only help so much in terms of box office in my opinion.
If i remember correctly, Batman begins-while successful, didn't really set the box office records on fire.
When or if Marvel decide to make a sequel to this Hulk movie, then we can see whether the Hulk is a franchise player or not.