A lot of developer driven organizations are very happy to outsource complex parts of development to managed services so they can focus on their core differentiators, especially when it comes to parts of the stack that need super high availability and security. This is why Auth0/Okta are big businesses and not everyone rolls their own key cloak / shibboleth instances, as one of many examples.
This clearly seems like the Apex/Drivewealth model but for challenger banks or new online banking operations. It is hard to predict what startups or new projects will need this because those platforms can unlock innovation for new categories (e.g. no one imagined commission free trading in 2008, and Robinhood wouldn't exist without Apex).