For banking specifically, you have the Open Banking initiatives around world, including the PSD2 directive in Europe, which requires that APIs for banking should exist and be offered to all.
There is no regulation or other government directives requiring social media companies to provide APIs open to all.
I know about PDS2 which is why I specifically bring up the example of Teller. They literally use mobile clients and reverse engineer banking protocols manually then expose them as APIs to their customers.
Just shows that tech is more scared of Facebook than massive established institutions.