Right, but that was the point of the episode of the documentary. At a basic level, American cuisine is based on plentiful food sources, and we get things like burgers and hotdogs. I recommend watching it, it was quite interesting. I'm not trying to suggest that this is the only explanation, but it was an interesting theory nonetheless.

Sure, some regions have some variety (as you mention, a casserole). Size is a factor, but similarly maybe countries have some form of culinary identity (russian, chinese, brazilian). They have sub cultures as well. I'm not well versed in them, to be honest, but i know they exist.

It was an interesting point that i found to be somewhat profound especially as i explored other cuisines, which are typically developed during hardship.