1. Most big banks require a ton of red tape to use those APIs. Even if you're using modern technology with a top tier dev team, this is still a 4-6 week endeavor at its absolute quickest turnaround.

2. All ACH transfers, for example, have to clear the Fed, which is done via FTP.

3. The consumer use cases are endless (make payments, analytics, etc). Just look at Mint, Truebill, etc.

4. The commercial user cases are endless (treasury management, AP, AR, etc).