[ardecila]

I think it's just that these regions are so gigantic and sprawling that they can't really share a unified culture. Natural boundaries or political ones tend to divide even people within an MSA into different subregions that identify differently. I don't think LA is unique in having different subregions and cultures, roughly broken down along county lines.

I feel like a fair bit of this is racial - white outer-suburbanites don't want to self-identify with the majority-minority core cities and first-ring suburbs. But race isn't everything; white New Jerseyans aren't objectively very different from white Long Islanders, but they would never group themselves together.

Of course, these same regions tend to come together over sports, etc so clearly the differences aren't irreconcilable.