Cause you're less likely to take your kids to see it and the amount of people going multiple times will be cut in half. Ben Hur, Lawrence of Arabia, The Godfather, Apocalypse Now, Schindler's List, Braveheart, anic, Lord of the Rings. Those are things of the past. If something as popular and rich with material as the Marvel universe can't bring about a 3+ hour movie, whether due to lack of writing skills or studio tampering, then nothing can. For s sake everyone whines or at least talks about a movie's length when it's around 2 and a half