The same system - Sanifair - is also active in the UK; last time I was in Germany, they cost 70 cents per visit - extrapolate that to the amount of visitors / hour and I think you get a decent wage to keep the toilets clean at all times. In addition, you get a coupon worth 50 cents, which can be spent at all gas stations / truck stops using the same system (most of them), incentivising making a purchase to help cover more costs.

In addition, the bathroom areas are designed to be easy to clean and brightly lit.