In days of old when folks where bold.....
Diesel engines needed a good long warm up time.. Gasoline engines, however, if allowed to idle for too long fouled and ran bad.. They needed to RUN. not idle.
Today... Thanks to many things including government regulations
Letting a Diesel engine idle for long times fouls the engine so it does not run right. Increases exhaust emissions and otherwise does bad things.
Fuel injected computer controlled gasoline engines can idle all day.
SOME. have learned this. But many RVers are older folks who learned in their Teens, as I did, and never bothered to re-learn... Others.. Well clearly I relearned.