What you pay for at a KOA is consistency. Not exactly the same experience at every one, but a known quantity. In the days before park review sites and apps, it was a way for people to not worry about the quality of the park and its residents. $60 a night certainly keeps the riff-raff out :)
And remember, most of the KOA parks were privately owned at some point, and for the post part it's the same people running the park. It's a good way for the older run down RV parks to infuse some money into infrastructure.