Because logically I should give tips to every service worker I interact with that makes min wage. I'm obviously not going to do that. If I do tip some category of service workers, it's certainly not going to be the ones that eat/delay/spit in my food as a get back for not tipping them, and it's certainly not going to be the group that makes well above min wage (I. E waiters are the highest-paid min. wage staff).