I was told that the use of 12 volts stems from when RV camping was camping. That is you needed a stove, lights, refrigerator, water and a heater.
So early on you find Stoves mostly gas, lights gas or 6 or 12 volt electric, refrigerators were ice or gas/12volt/120volt, water pump was manual or 12 volt, the heater as gas with a 12 volt blower if any.
There were variations on the themes but AC, Microwaves, Televisions and other high current devices were best served by the 120 line voltage. These conveniences from home introduced the populous to modern RVing. Still the Industry was a whole usually adheres to the self-contained philosophy. Your TT can provide the basic functions for a day or so if needs be.
The beauty of modern RVing is it can be adapted to what ever style you prefer, from remote boon docking to full service multi-week resort style gatherings.
If you want, somebody will provide it.