It's a pretty familiar story: studios and distributors are risk-averse and find it easier and more profitable to limit consumer choice and shape consumer preference than innovate. Once Jaws inaugurated the high-profit blockbuster model, and the multiplexes demolished the smaller theaters, there've been only slight modifications since. Is there more to it than that?
All that inside baseball stuff about whether its directors or editors or producers is beside the point, is it not? No one in the game has any incentive to make anything good, so they don't. People who are good artists, but bad salesmen, get weeded out. Even the most enlightened and hands-off producers have to turn a large profit or they sink.
I blame capitalism (shock horror).