The bank is trying to authenticate you, while you're trying to authenticate the bank. The bank calls and tries to authenticate themselves to the callee by saying "is your birthday such and such?", they're risking sharing PII with an unauthorized third-party. The solutions are a non-trivial amount of effort that no one really wants to put up with, unfortunately.

I used to have a residential mortgage with two other people and my name was stuffed into some ancillary field as a co-holder and they refused to give me any information or transact over the phone. I eventually figured out I needed to tell them to look in some extended info field, and the whole endeavor was annoying but ultimately I was appreciative of the strictness (that the entire mortgage data model—at the time (25 years ago), I don't know what it's like today—seems to assume that it will only ever be two people of opposite gender who are married will be on a mortgage was much more disappointing. The other two people were assumed to be married and the woman was seemingly by default listed as the non-primary).