Part of the issue there is that for a large number of people the ‘few times a year’ are major holidays when everybody else wants to tow their house-sized RV and boat to the lake for a day or two. The rental fleet just isn’t big enough to service the surge demand.
Can’t forget the boat! For reference, while this isn’t typical, it’s not uncommon. That’s a pretty small travel trailer and boat. I’ve seen this setup with much bigger trailers and boats several times.