Banks certainly have toilets, just not public toilets in most cases. It probably relates to several things: Customer time in any bank is very limited and the bank is actually better secured if that short stay is not lengthened. read more
The bank toilets are generally going to be available to the teller staff. It would not be practical to have two sets for tellers and customers or to require that tellers leave the secured area to use a public toilet. Toilets in banks do not give them a competitive advantage as they might in a grocery store, filling station, or coffee shop. read more