Which supermarket are you talking about? And how do you know what they think? I think we are applying economic theory, in which there arguably shouldn't be prejudice, to reality, where there is lots of prejudice:

Businesses have a long history of giving rats asses and much more about who their clientele is, demographically, ethnically, racially, socially, etc., and IME and in many public examples, many still do. I've seen discrimination, subtle and overt, against people who are young, old, rich, poor, black, brown, fashionable or not, speaking a different language, etc. etc. etc.