KOA is a franchise system and almost all the parks are owned by individuals. (there are a few owned by KOA corporation, but not many). KOA does not set the rules for individual parks. I don't know why such a policy was established. Could be they have a limited number of 50 amp sites and want to keep them available for rigs that need 50 amps. Could be they charge extra for 50 amps and in the past some people have said they were going to adapt down to 30 amps to save the money and as soon as the host disappeared out of sight, they removed the adapter and started using the full 50.