Do they even have business class on domestic flights anymore? Maybe like LAX to JFK, but I haven't been on a plane in the last 5 years that has 3 sections domestically.
People don't "avoid" first or business class. Usually they don't take it because it's 2-3 times as expensive.
When I fly anywhere that's under 2-3 hours, I don't fly first class. Anything longer, and I try to. Free booze, early boarding, free meals, special check-in line, special security line, and internationally, I get access to the Lounge. It literally saved my life one year coming back from Europe and got horribly sick on the plane. Being able to curl up in a ball in the Lounge kept me from going to the Hospital in Atlanta.
I guess a disadvantage is that everyone stares at you sitting in first class when they board to go back to coach.