"Living in America I miss the British sense of humour, that cynicism and sense of realism. It's almost impossible to explain to people. If you say something to Americans, they believe what you say. How ridiculous is that? They take you at face value, so I have to have these injections of ironic sanity to keep me on an even keel."
Richard Thompson in The Guardian.
It's not the sense of humor but this perceived value to bluntness, to face value. How often do you hear people (Americans) saying "straight talker" as a synonym for "truth teller"? Praising somebody who "tells it like it is." Of course they're wrong - it's far easier to lie with a blunt statement than a more elaborate one because the detectors come up for the elaborations.
So the point is that in show after show after movie after movie you have characters talk with nothing behind them. At any moment they'll launch into a description of their motives which are invariably correct. They act like particles in a physics equation. This is even when the motives are so blatantly obvious you'd figure a beginning screenwriter would muss them up a bit instead of actually underlining them.
In a commentary for an ep of The Sopranos David Chase remarked how fun it is to write a show where everybody lies and that's become a kind of touchstone for me. Not that characters should lie but don't real people do things for reasons they don't understand? Or their reasons are conflicted, distorted, mere justifications or even outright wrong? I'm not pushing "realism" or even a pointless notion like "well-rounded characters" so much as simple dramatic interest. And it's worth noting that what I'm describing is pretty rare in American films up until maybe the 60s and then slowly increasing so there's clearly a commercial motive that's trying to make the works as streamlined as possible.