The main problem in Germany is that banks "for the masses" (oversimplified) are "state owned" or cooperatives. Both are organized on a city level. Both are notorious for not cooperating. Plus the state owned banks usually have politicians at the top (E.g. the major of the city the bank is in).
For a system that works across Germany you would need a high level of cooperation.
In the 90s when I was a Sparkasse ("state owned") customer studying in Baden Wurttemberg but having my Bank in Bavaria, I needed to go to Bavaria to get money and account statements every time, the Sparkasse in Baden Wurttemberg would not cooperate with the one in Bavaria.
Not sure, it might be an outcome of federalism which is (was) a way to prevent the 4th Reich.
For instance if the Cash Group banks came together behind a mobile and online payment solution, the Sparkasse would need to follow suit.
Because the interpretation of cartel law and the banking structure makes that complicated.
They created "giropay" which is quite complicated as a dealer has to pick a bank to contract with and they get different rates and stuff as they couldn't simply create a shared company running it or something ...