Tragedy of the commons. Just try using any free toilet at a highway rest. Last time for me I could not have used the urinal without standing in a puddle of dark yellow piss. People are assholes. Not all, but most. At least if nobody is looking and they can get away with it.
The only reasonable reason why not, would be that it would be impossible to do so. If you are physically able to add those accomodations and not doing it then well you are a bigot that makes people's lives more difficult on purpose.