They could be defeated in multiple ways, as can most business models... good and ugly. The ones that exist are the ones that survived.
That said, they exist because it works. There's no way FB could make the money it makes by selling its product to consumers, but it can by snooping, manipulating and advertising. Banking goes in cycles and modes, but it's one ugly after another usually. Maybe they make steady, risk free profits while externalizing long tail risks. Maybe they enjoy a low competition regulated market that lets them fleece captive customers. Etc.
The oldest law codes we have show evidence of bankers being bold, usury and whatnot.
In a lot of the big, egregious examples (FB, Citibank, etc.)... killing the abuse would be turning a $1trn industry into a $1bn industry. It's certainly possible to do social media or consumer banking in a much smaller/cheaper way.