The problem is that theater owners HATE long movies, and their guild is powerful.
You see, when you pay your $10 to get in to the theater, the owners know you'll be out again in just under two hours. That means that from 11:00 AM until 11:00 PM, they can have six showings of the movie, thus earning $60 per day per, ticket seat.
If they have to host a 3-hour movie, then they can only have FOUR showings of the movie. That means they earn $40 per day, per seat. That lowers that screen's value by $20 per day, per seat.
That's ONE seat in the theater. Now, when you're talking about a theater that seats 200 people, you're talking about the difference between earning $8,000 per day (3 hour movie) versus earning $12,000 per day (2 hour movie). For a week's showings, on a blockbuster film, that's $28,000 LESS the theater will make, just because a director made a three-hour film instead of an theater-approved, industry-standard two-hour film.
Yes, it cripples creativity. Yes, it stinks. No, the studios don't care what you want. They will appease their theater owners guild no matter how many signatures you get. The only way a longer movie shows up is if the director contractually stipulates that the length of the theatrical version is up to him, or something of that nature.
You want a three-hour movie. I want a three-hour movie. The owners of Goodrich, Loews, Loeks, and every other major movie theater chain absolutely DO NOT want a three-hour movie.