You're confusing two things. A distribution deal is not a license. Licensing is different. Fox for example, holds the license to make X-men and Fantastic Four movies, and they produce and distribute those movies themselves as long as they hold those license rights. The license rights expire if certain terms are not met, because no one would license something like this without such terms.
A distribution deal is different. For Hulk, Marvel Studios was the license owner and they produced the movie. Universal was just the distributor helping get it into cinemas because Marvel Studios at the time did not have the infrastructure to do so (they still don't, but since they're owned by Disney that solves that problem). As such, it is likely that when they signed on as a distributor, they have first refusal rights to distribute any future Hulk film made by Marvel Studios, and such deals are common for franchises as a sign of good faith when you want someone to distribute a film for you. Paramount had the same deal with Iron Man but Disney negotiated those back. They clearly don't feel Hulk is valuable enough of a solo character to do the same negotiation with Universal, so it's not really just a case of Universal not wanting drop what they have for cash, Disney might just not be interested.
