There's a secondary cause mixed in here I'd like to propose. If you were to pay forward at this Panera, you don't know where your money is going to. That alone

There's a secondary cause mixed in here I'd like to propose. If you were to pay forward at this Panera, you don't know where your money is going to. That alone would make you hesitate as a consumer: You're not sure whether you'll be paying forward for someone who is in extensive need of the meal, or just a well-off customer who's looking for their discount-of-the-week for a decent sandwich. It's the same kind of unease that pushes people away from giving money to panhandlers: they want to know that they are actually helping a person survive, not enabling them to seek out the means that may have contributed. (No, that's not what all of them will do. The point is you don't have the information and you will tend to err on the safe side in that context.)