Some banks and corporations said theyre halting purchases of Bitcoin and other cryptocurrencies on their credit cards. Banning it because they dont want the credit risk associated with the transactions. Some says that allowing purchases of cryptocurrencies can create big headaches for lenders, which can be left on the hook if a borrower bets wrong and cant repay.
Not necessarily banned in all banks, there are some banks that accept bitcoin and other cryptocurrency like in my country.
Maybe, one of the reason why the banks prohibited the bitcoin because bitcoin is a volatile and the banks don't want to risk theirselves and the lenders. The banks also think that if they will incorporate bitcoin in their system, maybe anytime they will lose profita that may lead to their bankruptcy.