People think that petstores are cruel b/c they keep bettas in cups?

ONE BETTA NEEDS A MINIMUUM OF 2.5 GALLONS IF NOT 5 GALLONS1!!! that i know. but why do people tink it is cruel for petstores to keep them in cups??? they have no other option. they are fishting fish. what would you do if you sold betta fish? you woudl have to use cups. and it would be really expensive to give even each betta a 1/2 gallon tank. so why are people so against it? its not fair but as long as they go to good owners (which they dont most of the times:( ) what would you do if you ran petsmart or petco or whatever!?