The federal reserve doesn't want zero risk banking where end customer is effectively 100% on their books, and will deny accounts to any bank that functions the way your service would would work ( see the denial of account to The Narrow Bank ). It's against their monetary policies as it destroys the mechanism by which credit expansion happens.

> “pose undue risk to the stability of the U.S. financial system and would adversely affect the Federal Reserve’s ability to implement monetary policy"

https://www.chicagobooth.edu/review/safest-bank-fed-wont-san...