As mentioned on another thread, the UK enforces such an API for the largest banks (it's voluntary for the others at the moment) https://www.openbanking.org.uk/

This is part of a wider "challenger bank" initiative. Creating space for smaller, usually digital only, banks to create more competition in the consumer banking market. This was thought to be especially important after the "too big to fail" crash. Directly breaking up the larger banks was never going to happen, so instead they created an environment where competition could (hopefully) flourish.