I agree, but they have every financial reason to keep doing it. How would you convince them to sell one product for one price to everyone for less total money?

Usually such crookedness can be avoided if competition is high enough. I.e if competitors can be profitable without ripping customers off, they could do that in order to attract customers to their option. Seeing that they are losing customers, those who resorted to price discrimination start thinking about restraining their greed. Unfortunately when completion is weak, or all participants agree on using this crooked practice to keep the prices high (which should be illegal really), they get away with it.