They privatized upkeep on rest areas a while back. I don't know if they took it back to state control again or if the private companies got better, but when they first switched over, the frequency and quality of the maintenance plummeted. There were a number of stories on it in the media. Trash went un-emptied and consequently litter blew all over the place, stopped up toilets remained that way for multiple days creating vomit-inducing odors, etc. They seem to be better now, at least the ones we've patronized.
I agree with some of the other posters...if we're not getting gas or a pop, I feel uncomfortable using the restroom at a business. I prefer rest areas, as they are dedicated in & out situations, parking is easy, and there are multiple stalls if you're in a hurry!