There re several online services where you can get interest on your BTC. Not a registered bank though. There s no 100% safety.
Nobody likes services that do not give useless secrets to our savings. That is why such a bank will not be popular.
although bitcoin bank there. I think they will not get a lot of users
a bitcoin bank will always be another service like many other services out there that are offering something about bitcoin, and you are right it would be centralized and because of that many will never use it but also a lot of people may actually use it because of all the services that a bank offers (the same services that they offer for fiat and we use)