Because its an obvious failure. If Marvel wanted to produce more Hulk films, they easily could (like Spiderman), they don't though because there is no money in it.
Well, they had one franchise in the initial Phase 1 roster that had a film before and it was the Hulk (the worst performing film in the lot). I've said this before too, but the most successful superheros nowadays are the new ones. The rebooted films (Spiderman, Superman, Batman) tend to do worse than their contemporaries and even their initial outings.And while Ascended shouldn't have used the phrase "right out of the gate", it doesn't take a genius to infer they meant Marvel laid a good foundation with characters who didn't have the popularity (like some of their other properties).
The reason why I'm so ornery about this is because certain people always view the initial MCU films with rose tinted glasses, portraying these films as indomitable from the very moment of their conception. As a DCEU fan, I've had to ensure relentless screaming that the DCEU is a failure when the initial MCU films are arguably less successful.