Rats are wild animals and can live most anywhere. It is not unusual to see rats in my backyard here in Texas, and I live in a rural area on 2 1/2 acres, so they aren't the result of human overpopulation here. Add the resort and messy people who drop food and feed the other animals, and the rats will be there. I don't know what you expect Disney/
DVC to do about rats on the outside of the buildings. Except maybe bring in some feral cats, like you see around Disney Springs. Snakes and feral cats are the best way to control the wild rodent population.