A better analogy than the pizza analogy might be a "customer" repeatedly buying clothes with the intent to wear and then return them. Despite the fact that there is a return policy in place, the fact that the customer never intended on keeping any of the clothes makes his behavior fraudulent.

In the case of a real restaurant, yes there is harm done. The cost of taking an order is not zero for people: it cost people time and real customers may not be served in time. Maybe not for this particular case with Gett since they're automated.

You could argue that there was no harm to Gett because of the cancellation fees, but that's only true if the cancellation fees are greater than the cost they incurred which may or may not be true.