Yes, security/privacy. Banks are heavily regulated, and "I can't avoid them to store my data" anyway. (I do mostly use cash, much to the irritation of shops these days.) I have multiple accounts, which I manage offline without giving any third-party service access to them. The transaction data for my bank accounts is not very interesting thanks to me doing most things in cash. I don't need banks (or credit card companies), tax authorities or tax advisors to know how I spend my money, where I eat, what kind of services I enjoy.

I would however have an interest in some of what these fancy new "let us have access to your account" companies are offering. If it was simply software to use 'offline'.