A partial answer is also the US's approach to banking regulation. First off, the US prioritizes having many small community banks. The US has 4,909 banks, while Japan has 198. This necessarily makes setting up inter-operation between banks more complicated.
Second, US banks are regulated on both a Federal and State level. A system that works for a bunch of banks in California may not be viable for interoperation with banks in, say, Georgia.
In short, US banks cannot easily set up a way cheaper system with the vast number of banking partners they'd need to coordinate with and the large amount of regulatory systems to navigate.
> The US has 4,909 banks ... This necessarily makes setting up inter-operation between banks more complicated.
The EU has 6,250 banks though. Each with different countries. With 28 different languages, cultures and governments, with far more differences than the states in the USA.
You're really arguing that it's harder to unify that in the homogeneous USA than it is in Europe? Come now.
In the UK there are Building Societies. Originally the concept went only like this: If a thousand workers in a town pool their savings to form a mutual Building Society it can use that money to loan someone (one of their number or somebody else) money to build a house. The new house owner's payments on the loan provide good interest on the savings and a profit the society can use to expand, as savings and loan payments roll in they can loan more money for another house and so on, eventually everybody gets a house and rich bankers get nothing because the society's savers and borrowers are also its owners. The first ones were Limited Building Societies, they ceased to exist after a period of time having served their purpose - providing loans within a geographically constrained community, but the Permanent Building Societies grew, and eventually came to dominate mortgage lending as an industry in the UK.
Towards the end of last century unfortunately there were what the press called "Carpetbaggers". The carpetbaggers realised that a Permanent Building Society has a considerable cash reserve because it needs to be able to survive a "bank run" and its main assets are other people's homes which aren't liquid enough to cash out if a run happens. Their plan was, join the society and then vote as members to convert the society into a limited company, an ordinary bank - effectively cashing out. This worked on a number of famous Permanent Building Societies, including the one that had loaned money for the house I was growing up in at the time. I voted against, my parents (whose mortgage it was) voted in favour, and their side won, the society no longer exists. Some societies instituted "anti-carpetbagger" rules to try to prevent it, challenged demutualisation in the courts, or just plain voted against - those are still successful today, while the ones that turned into ordinary banks were mostly ruined in the recession (e.g. Northern Rock)
Edit: I also nearly witnessed a "carpetbagger" situation at a local credit union (where leadership wanted to become a bank/corporation), which was voted down.
Yes, the credit union is very similar in practice, although there are numerous technical differences. The most obvious practical difference was that originally Building Societies were oriented around this idea particularly of loans for members to buy homes, a worthy goal that is also conveniently economically sound. Credit unions are broader in scope from the outset.
It was perhaps more obvious (especially for the Limited Building Societies) that they've achieved something good if now everybody owns a home, whereas if now everybody has a savings account with the credit union, er... is that better? Maybe?
As a member of the society you "own" it but you can't sell that to anybody. Demutualising creates a new public company with shares, which naturally go to those owners. The shares in a public company can be sold. The exact rules for how shares are divided among members would have been in the terms of the proposed demutualisation.
I can probably look it up but I received a not inconsiderable sum of money for my shares when I sold them many years later. I presume my parents sold and spent the money very soon after the plan went through. All members received shares (it would be obviously inequitable to propose that only those voting for the deal get shares if the vote passes, I'm not sure if that would be straight up illegal, but it would clearly be immoral).
Second, US banks are regulated on both a Federal and State level. A system that works for a bunch of banks in California may not be viable for interoperation with banks in, say, Georgia.
In short, US banks cannot easily set up a way cheaper system with the vast number of banking partners they'd need to coordinate with and the large amount of regulatory systems to navigate.