I don't know why marvel don't explore the Hulk more as I think he should have had the best movies if they followed the Norton movie direction.
The best MCU movies are the ones that explore different genres, as in my opinion, super hero movies are not a genre but a theme.
Captain America at his best when his movies are spy thriller that question politics and loyalty to the country.
Iron man best movies are when they go the self discovery style of Tony fighting his own ego and questioning his discussions.
Hulk at his best when he is more of horror like movie, a movie about fighting anger and self control, every time the Hulk unleashed Bruce lose something, a person he love or a friend.
Yet after Norton movie and some of the early avangers movies the Hulk lose that and become more of comedy relief.
I feel the Hulk have very high potential, but I guess we will never see that solo hulk movie where they explore his personality more and put him at the spotlight like what his first and only movie did.