A lot of that could have to do with film quotas that require cinemas to screen a certain percentage of ‘local’ films, regardless of demand and thus leaves only the most profit-generating American films available. Film quotas, while they sound good, result in essentially the subsidization of sub-par national films since they don’t have to worry about competing with the rest of the world; it essentially lowers the bar because these films don’t have to compete for screen time against so many, often better, foreign films.
Note, I am not saying American films are the best, I am just saying that film quotas make it easier for mediocre films to be exhibited because they aren’t competing against a full slate of imports. Look at the current French film industry as an example — pretty much crap except for the occasional standout. Although to be fair, the quota system in Korea actually resulted in a pretty vibrant cinema industry, but that seems to be an exception.