Chris Evans originally signed on to play Captain America in six Marvel films. This means that Avengers: Infinity War would have been his last movie. However, Marvel asked him to come back for the fourth Avengers film, which he agreed to. While talking to The Telegraph, Evan explains why he decided to stay on for a seventh Marvel movie, saying:
“I had six films in my Marvel contract, so I could have said after the third Avengers I was done, but they wanted to make the third and fourth Avengers films as a two-parter. They said they had so many other characters to fit in – Guardians of the Galaxy, Black Panther, Captain Marvel, Doctor Strange, Ant-Man – and couldn’t get them all into one movie.”
He went on to say that he agreed to do the two-part Avengers story arc, “because it made sense. It’s going to wrap everything up.”
When he says it wraps everything up, I imagine he means that it's going to wrap up everything that the MCU has built in the cinematic universe so far with The Avengers. Marvel Studios President Kevin Feige has said in the past that things will be a lot different after these upcoming Avengers films. He said the MCU will be a very different and new thing:
"Certainly, as we get to Infinity War there is a sense of a climax if not a conclusion to, by the time we're at untitled Avengers 4, the 22 movies that will have encompassed the first three phases of the MCU. And what happens after that will be very different."
I can't even fathom the kind of craziness we will see in the MCU by the time we get to Avengers 4. I just hope that it all ends in a way that is going to surprise and shock fans, and also leave them happy, satisfied, and excited to see what they plan on doing next.
Avengers: Infinity War hits theaters on May 4th, 2018. Avengers 4 will be released on on May 3rd, 2019.