I think part of BBQ's roots come from being a cheap meal made from shitty cuts, and I suspect that a lot of this stuff has simply been carried over generation to generation. I mean growing up that's how I remember BBQ being...cheap white bread served with mounds of meat and sauce, all thrown on paper/paper plates on a cafeteria tray. And a lot of these places were literally shacks in some cases, or at least run down. I'm not sure if it's correct, but I also felt that for a lot of people opening up a BBQ joint was more of a way to make a business out of a hobby and many invested what money they had, so it wasn't like people were turning out Michelin Star BBQ places.
White bread...I agree that it's for mopping up sauce (or as edible napkins!), but I know people that like to make their own impromptu sandwiches with it, or using it like you'd eat Ethiopian with your fingers and Ethiopian bread.