Banks in the US use Open Banking APIs too, they won't open it up for the public to use, though. Every company, not just banks, wants us to have their app on our phone.
I was developing these apis for one of the biggest banks in central/eastern Europe.
You’re right that they are not intended for bank to customer access directly. What they allow though is for third parties (other banks, mobile apps, services) to access these apis. It requires a licence though.
Point is that a lot of banks in Europe allow to add other bank‘s accounts to their app. Also aggregator apps exist.
Banks could simply come together and develop an open banking standard for customers. Would probably save them a lot of money too, since the development of their stupid apps presumably costs them a lot.