News alert, banks do not transfer bitcoins. Banks do not hold bitcoins in their accounts. Banning their use in their banks is meaningless.
bigger newsflash , Banks are more involved with Governance then people imagine. One can be used to exercise the will of the other, and often happens. But hey, you are right, they can't "write" into law their own stuff, but their lobbyists can. and if you can't use the technology at the FIAT point of exchange, you are handicapping the convenience, and therefore the adoption by users.
Let's take it up a notch.
Banks don't think or do anything. Governments don't think or do anything. Individual people within banks and governments guide these institutions.
There are plenty of individual people in both banking institutions and governments that are PRO Bitcoin and changing their FIAT for Bitcoin.
Create more Bitcoin followers in the banks and governments, and the banks and governments will support Bitcoin. (If banks and governments "do" anything.)