They wont do that if they can sneak a lead out to the vehicle.
Again, simple!
Ah, you've got an EV? Yes, that'll be an extra $"10" / night, thank you!
And then who pays for that ?
The same people who paid for the toilet block, camp kitchen, rainwater tanks, landscaping etc etc etc. The Park puts it in, because they'll make the money back to cover their costs. Same thing with Parks that have their own fuel pump installed (usually with bloody expensive fuel!

) - noone forced them to do it, they just did it to provide an extra service to their customers.