There is virtually nothing stopping us from seeing any movie we want. You can go through Netflix, Blockbuster, a local video store, a chain movie theater, an independent movie theater, a repetertory/revival house, or Amazon. You can watch films online. You can buy a non-Region 1 DVD from another country. With a little elbow grease, you can watch anything.
So how could that possibly restrict what we watch? First, bear in mind I'm not talking about cinephiles here, who do seek out all the Region 2 DVDs of obscure foreign films, but rather the average moviegoer. My theory is the "it's what's for dinner" theory.
Say it's April 1952. You feel like seeing a movie. Unless you live in New York or LA, Singin' in the Rain is pretty much your only option. If you want to see a movie, it will be Singin' in the Rain. If you don't want to see that, you won't see a movie. It's what's for dinner, take it or leave it. So you go. Most people probably wouldn't be against musicals - or any genre, for that matter - because there weren't enough options to just rule out a genre. Teenage boys who now would only see Transformers and The Hangover would see musicals, romances, historical epics, foreign films, anything back in the day. (Let's not forget that for a while, foreign films were the exclusive source of on-screen nudity and sex.) You just liked cinema in general.
Now, if you so desired, you could restrict your viewing habits so that you only watch Mexican zombie movies, or only movies with redheads. There's no need to see something that isn't EXACTLY to your taste, unless maybe a friend or significant other drags you along. Americans also aren't inherently adventurous in their entertainment. Entertainment is a form of comfort, and most people stick to what they know. It's like how foreigners will sometimes remark that in American supermarkets, the variety is insane - there's like 200 kinds of ketchup. But that doesn't mean that Americans go through and systematically sample every kind of ketchup - they find one that works and stick with it.
Maybe the French New Wave gained traction in the U.S. - or anywhere - because these films would only be one of a few options you could watch on any given night, so people gave it a whirl. Hell, maybe that's how any movement gained ground. I'm not trying to make any value judgments here, because quality very rarely correlates to popularity, but just looking at the trends I'm not sure it would be the same story today.
What do you think? Has the smorgasboard of options caused us to retreat into niches?
P.S. - Don't get me wrong - not every movie was an automatic smash under the old system. It still ultimately had to appeal to viewers on its own merits. But by virtue of any one film being the only game in town, it could put asses in the seats on opening night. If the crowd liked the film - even if was something that might not have appealed to them on paper - they will tell their friends, and it's a hit. Now, there's no way to force asses into the seats, so films don't all get an equal chance.