I see you don't understand the network effects of banking. Many people can't switch banks because of commitments like home, car and personal loans which in the majority of cases don't seamlessly transition to their new bank. It is such a big issue that many countries e.g. Australia, UK have actively put in place policies specifically to address it.

And my point still stands that the overwhelming majority of people are comfortable with their most private data being in the hands of third parties. And Facebook has long reached that point where people can trust it for managing their semi-private data.