You can also think that banks can start offering their customers bitcoin and crypto if their central banks allow it. Compare bitcoin to fiat and not bank. Also bitcoin is an alternative to fiat and not a replacement. Just know that bitcoin can not replace bank at all. Also it can not replace fiat but you can use it as alternative.
You get it. Bitcoin is money, banking is a type of service. You can't compare these two at all. What can only happen is that banks adopt Bitcoin for everything as well, but not as a replacement of fiat but an addition. It would be similar to just like adding another fiat currency to the portfolio that they already have.