FitzTheRuke
Legend
I think the answer would be: Because a lot of people find those scenes fun.It utterly baffles me why DM's insist on faffing about on a bunch of completely forgettable, utterly trivial scenes. We are at point A. We need to get to point B because that's where our adventure is. Why would I bother wasting the table's time on talking to random stranger who has nothing to do with the story?
I'm a little with you (though not nearly anywhere as extreme): I like to throw in a line or two of fluff in those sorts of scenes, but I don't prefer a lot of in-character back-and-forth in funny accents. I'm okay with it when a player likes it that way, though - it's a well-loved way to play D&D.
And like you say, my ego isn't important enough to me to have play be "my way only" - not here, and not even at my table, not as a player, and not as a DM.
Naturally a table I DM at will lean toward my preferences, but I've certainly played with method actor-types, and I'll interact with them as long as there isn't someone who feels your way, getting too bored. Though you'd have to be patient and put up with a reasonable amount of it.
All of this is what I call "Playing Nice With Others". I think that there's room for everyone, as long as they're willing to work with other people.