“Restrooms for Patron’s Only”
Because it costs too much to let other people use it. Then you might have to let everyone use it. I’m sure the cost per flush on that bathroom would bankrupt you. The cleaning process would overwhelm your labor costs. The toilet paper costs would throw off the ROI of people using your bathroom.
Or you just don’t want to deal with all that other stuff, so you don’t. You tell people ‘No’ unless they buy a pack of gum or stick of beef jerky.
Most people won’t. They will walk up the street to your competitor, use their bathroom, and probably end up spending more than they would at your establishment. They might even make a meaningful connection to the clerk who is focused on saying, ‘Yes.’
But at least your bathroom is clean and readily accessible.
Where are your priorities a little cockeyed due to a social norm? Where are you saying, ‘No’ where you could be saying, ‘Yes’?