Iron Man was and remains one of the most iconic characters in the MCU, which raises the question of why Iron Man 4 never happened. Robert Downey Jr.’s Tony Stark kick-started the MCU and was the only hero to star in two solo movies before The Avengers (2012) wrapped up the MCU phase 1. RDJ later headlined Iron Man 3 (2013) in phase 2, but a fourth movie never surfaced despite Tony remaining a central figure in the franchise for another six years until his death in Avengers: Endgame (2019).
It seems as if the idea was at least entertained, as negotiations were reportedly happening around the release of Iron Man 3. RDJ, Kevin Feige, or anyone else at Marvel Studios has never given an official reason why Iron Man 4 didn’t happen. However, looking at the circumstances around Robert Downey Jr., Iron Man, and the wider MCU provides some reasonable insight into why Iron Man 4 didn’t work out.
