The same thing will happen with insurance companies, especially if they are forced to cover pre-existing conditions and can't guarantee a certain number of healthy customers to cover all the sick ones.
Why don't we eliminate all fees, penalties and taxes while at the same time maintaining the world's finest military, repaving all the roads, reinforcing all the old bridges, building more dams, maintaining a decent court system and federal prison system, etc.
That wasn't because banks were allowed to do business across state lines, at least no directly. The fact that interstate banking had become universal was used to justify much greater intrusion into the industry by the Fed and other federal agencies. It has been the bank regulators who have been pushing and even forcing banks to consolidate. Bureaucracies like to deal with organization that look like them.