The Marvel Cinematic Universe is not called a film universe just because it is good marketing. It is a mega-series consisting of smaller series that happen to intertwine. There are three Iron Man films, three Captain America movies, three Thor flicks, and so on. Some of the newer characters in the universe, such as Black Panther and Doctor Strange, only have one so far.
This makes the case of the Hulk quite unusual: he had one standalone movie in 2008 and never had another. Many fans of the character find this a pity: that first Hulk movie, only the second in the entire MCU, is quite interesting for what it is, and looking back on it as a bizarre and rather a rewarding experience for any MCU enthusiast.