Answer from another: nothing. We also have them in various places, like parking, or highway vignettes - you are not using their facilities, you save them money, so they charge you some extra
I did some travels in places where bidets are common, here’s my take:
Check out the history of bird migration science. There was everything from birds going to the moon for winter, swallows burrowing in the mud, transmorphing to different species, up to the 19th century