Mandatory Access To All Public Restrooms in All Public Places

I have traveled the USA 3 times. Did 49 states in less than a year but when I have to use the restroom many places have signs that say "no public restroom" so after traveling a very long time and not wanting to show my body parts on the side of the road or get fined for littering I am upset that there isnt a public restroom in each town sufficient enough for people traveling. We have to use the restroom. Our bodies require us to rid of waste and we have no control of when we have to do so. Why cant these places be made to have restrooms and have them all made to be open to the public if they are open for business and without requiring you to make a purchase to use their bathrooms.