Developer Experience is important, and that includes much more than the technical design of an API. It also includes the documentation and support as well as the pricing and the legal licensing terms. In almost every API project I have been involved in the legal details have been slapped on last-minute, usually by a lawyer that does not know anything about APIs or technology.
There are also way too many examples of API licensing terms that are actively developer hostile, which does not really invite developers to use the API (assuming they read the terms of service that is).