the 10 year rule, how common is it and how is it enforced

We had an 11-year old trailer worth a few thousand dollars, and were never turned away from any campground. We sold it, bought a new 1-ton dually and truck camper - combined value somewhat north of $65K and have been turned away numerous times, especially back east as well as in Arizona. Seems like quite a few campgrounds don't want truck campers, regardless of how they look ar what they're worth. No one seems to know why.