Does anyone tip when ordering from a take out counter? Or picking up a phone order?

Was recently in LAS and I would go downstairs and place an order at a burger restaurant and wait on a bench for my order to be made. The order is punched in, when it was ready, someone from the kitchen which was 20-25 steps away from me would deliver it to the counter and I would be on my way.

Every time I would sign for the receipt (went twice) there was an option for a tip which I would always cross out. The cashier would roll his eyes at me.

As I walked by the restaurant one day, I noticed all of the workers in the restaurant; cashier, waiters, bartenders etc, were wearing t shirts saying, "Be kind, don't forget to tip your server"

I usually tip well but why would anyone tip in this situation?