I think it's like any evasion of payment. It happens because it is possible and because people think they are only taking from the corporations. The interaction is between the 'little ol' me with all my hard earned cash' and the big amorphous corporations. People can justify criminal behaviour because they are able to depersonalise the 3rd party being wronged. It may help if artists and their representatives can overcome that barrier between them and the people who obviously want what they do.
I think if people could see that their money made a difference or where it went they would be more inclined to be honest. If you know your ten bucks gives $6 to the corporation but $4 of that goes on development and future productions or whatever then you may be more likely to justify it as worth paying. At the moment people just see they can get the beneifit now 'free' if they steal. They don't see any consequences, or just wilfully ignore questions of right and wrong as the party being wronged is opaque and impersonal.