Dutchmensport mentioned on an interesting touch from the past. Many of the pre-WWII camper had: gas lights, gas stoves, gas furnaces, and hand palm powered water pumps at the sinks. No electricity at all in your 14 ft. abode, just LP.
Some of the early camper had large dry cells "lantern" batteries. Much of the time was spent outdoors cooking over a wood fire and eating by Coleman lantern.
There is nothing wrong with that, heck I do 18th century re-enactment where all our gear is pre 1800's and we sleep in lean-tos held up with the canoe paddles.
So the real answer to the OPs question is as I stated before, inverters are one more convenience of modern RVing. Some need then some do not.