I have heard of a number of CGs that say no AC units and no electric heaters. What is wrong is not telling you before you book the CG or it's not on their website. But in reality how would they catch you? We run our TT entirely on permanent built-in electric heating (on 30 amps) and don't use the furnace (could if we had to but it's so dang noisy).
We stayed at a Thousand Trails 2 seasons ago that said no AC units and it was around 100F out!! With AC units, I can see a voltage problem with a lot of RVs running them and it is technically possible that the CG main breaker or sub-feeder breakers could even trip. That was the Thousand Trails' claim and said it had already happened. If enough people were using autoformers as well, that would make the problem even worse at the CG main power distribution.
I would say a much smaller percentage of electric heaters would be used in cold weather compared to AC units in the summer. Sounds more like a penny pinching policy.
RV parks and CGs do not have electrical systems that are poorly engineered. The problem lies with the NEC code min. requirements. The latest NEC edition doesn't even come close to covering the power demand of RVs today as there are a lot more with 50 amp services and 2 AC units as well as larger and fancier RVs with higher power demands. Older RV parks & CGs had even waay lower NEC requirements for power load demand requirements. The older the CG you go to, the higher the chances of running into low voltage, few 50 amp pedestals and restrictions on electric heaters and AC units. Some upscale RV parks and some gov't CGs have electrical system designed above the min. code requirements. The worst CG we have been in to date is a Thousand Trails on the Oregon Coast - 106 volts before even turning anything on.