Why do some jobs pay $7/h when others pay $12+/h ??

My sister just got a job in California working for LDS family services.
Her last night in Provo we all decided to go to Café Río.
I had a card that was full of stamps that get you a free meal, so I handed it to the employee when we went to pay.
You’ll never guess the employee’s response.

“Which meal would you like to be free?”

I looked down, and on our tray were a few $6 burritos and a $10 quesadilla.
I then looked up at her, to see if she’d caught on.
I looked down at my tray again and then back up at her.
She looked at me with a blank face, still waiting for my answer.
I pointed, paid and left.