Why We Never Got To See Iron Man 4

For the nearly 20 movies that led up to the Infinity War, Marvel's strategy has been to release movies in three discrete "phases," each leading into the next one, ensuring no one ever feels encouraged to stop coming out to the movies. But the fourth Avengers is bringing something new to the franchise: a sense of finality. 

All of the original Avengers actors—Chris Evans, Mark Ruffalo, Robert Downey Jr., Scarlett Johansson, Chris Hemsworth, and Jeremy Renner—are reaching the end of their contracts with the fourth Avengers movie, and none of them are expected to return. It will be a definitive farewell, and now that the stakes in the overarching story of the MCU are so high, it's more important to have all of those characters take their curtain call together rather than waste an appearance on a Tony Stark solo movie.

As one generation of Avengers takes its bow, another is on the rise, with new heroes including Captain Marvel, Black Panther, Wasp, Spider-Man, and Doctor Strange taking center stage as the long saga of the Infinity Stones draws to a close. Call it a drawback of the shared universe if you'd like, but for the long-term survival of the MCU, it's more important to build out the entire sprawling franchise, not see if lightning can strike for a fourth time with another Iron Man.