If you have multiple front ends on top of a shared backend, like a desktop and mobile UI, as well as a bunch of third party integrations, then it makes a lot of sense to build the API first. The thing is that it requires three different use cases before you can make an API generic enough to cover the majority of the needs, and that makes it difficult to build the API first and UI later. I believe in the approach, but it's not the right way to go for everybody.