RedLetterMedia had a pretty good bit about this. The theory is that movies have so much competition from other forms of entertainment today that film companies have to bank on name recognition a lot more than they did in the past. The further back you go, the more likely it is you'll recognize a title. There was just so much less other **** you could do to occupy your time (Video games, Chatroulette, sofftcore Youtube porn, Jersey Shore, etc).
I think the writing talent has left the movies. Or, the industry is running zscared and trying to bring the money making films.