Well ... I worked for a company who dealt with lots of PII (like, info on *every* person in the US). We put together a system to monitor what TOR nodes existed, and compared attacks to TOR nodes. It was significantly used as an attack vector, not only because of the anonymity, but because the attacker could change IPs frequently. Not a single legitimate user used TOR.
We decided it was worth protecting our users, and the PII of everyone in the US, to refuse any traffic from TOR.
Banks doing the same thing does seem like it's in the best interest of the customers.
If you are a legitimate user, and some 3rd party logs into your account and transfers money out, would you prefer the bank to say "Sorry, it was some random person, and we have no way to find or prosecute them. They will likely do it again." or "The intruder was found and prosecuted."
Depending on the theft, you may or may not get your funds back. If someone goes in and transfers funds as you, some banks aren't willing to refund the transaction. Transfers aren't handled like credit card transactions, which are easily refunded.
Even if your bank does give you the stolen money back, that means they've absorbed the cost. So your loss ($1 or $1M) and refund, is now added to the fees, because the bank's operating expenses are higher.
I'd prefer the "inconvenience" of not being allowed to use TOR and other anonymous relays, and not have the bank have a huge and expensive fee schedule to make up for losses that are impossible to recoup from the thieves.