Things have changed. Superheroes' have to register with the government. In the past, superhero's with stand alone movies didn't share the universe with other superhero's.
Iron Man wasn't born in the first Captain America movie. Hawkeye and Black Widow worked for S.H.I.E.L.D so they were going to make cameo's like Coulson did in Iron Man.
And they made it clear that the Avengers only came together when they were "activated" in AOU.
At the end of the day, the Avengers Tower is in New York. He already fought with the Avengers and it was Tony Stark who discovered his identity so why wouldn't he be in this movie?
They even referenced civil war footage in the trailer. There are no more stand alone superheroes. That ship sailed 4 years ago.