Enterprise applications are usually so deep and far away from the database that building an API by hand, per se, would be nearly impossible. This product is targeted at those companies, not small, agile ones.
As someone who works on a deep and far away application I would have a hard to seeing how connecting to our datasource (which has been abstracted to hell by ORM layers) would be a better option for developing a rest interface than using existing infrastructure. That being said, I like the path they are taking and think it's a valid approach... just not sure how many people actually need it.
Building an API by hand is only impossible if literally no one in the organization understands their data. If that is the case, an API is the least of their concerns.