How transacting through a bank to move money on/off crypto exchanges could be "risky" for the bank? Unless banks don't want account holders to spend (or lose) t

How transacting through a bank to move money on/off crypto exchanges could be "risky" for the bank? Unless banks don't want account holders to spend (or lose) their money, to keep better balance sheets.. but banks shouldn't dictate what customers do with their cash. Exactly the reason customers want to be less dependent on high-street banks and keep their money/investments in a self-custody. Self-custody is the largest appeal of crypto currencies.