1) Why do so few characters in the movies shut the door behind them after entering a house/flat? In real life, I've only seen someone fail to do this if:
a) They are unloading a vehicle into the premises; or
b) the place needs airing out for some reason.
But notice (if you haven't already) how in movies and TV shows this practice is habitual, to the extent that I'd guess the door is left open more often than it is closed. Why would this be? The reason could hardly be to avoid losing time in advancing the plot! The act of swinging the door shut can be accomplished while walking through it.
Does Hollywood have some vested interest in seeing lots of doors ajar?
2) Why does just about no one in the movies exhibit decent table manners? For instance, why does just about everyone in films keep stuffing food in their mouths and then mumbling through the mouthful while having a conversation? Certainly there are people who act that way, but if the intention is realism, then a film ought to depict other characters who don't flout that principle of dining etiquette. However, note that this is almost never the case.
Does Hollywood have some vested interest in promoting poor table manners?