There are thousands of different CMS solutions out there. They all try to do everything, and fail.
What if i want the beautiful frontend of Ghost (with scalability and instant deploys), with a bite-sized editor (like Buzzfeed have), and a cloud-hosted content repository (Prismic)?
We need a standard. Standards let applications focus on doing one thing well, plugging in to other applications to take care of the rest.
In fact, there is a de facto standard for content repositories: the WordPress public REST API. WordPress powers over 20% of the internet. It has a comprehensive and well-documented posts API, and a mature implementation.
By using a standard API, vendors and publishers can move faster which means a better experience for end users. What’s not to like?
(NOTE. There is already a standard called CMIS. It’s enterprise. It’s XML, not JSON. It has a spec so long that probably no-one has ever read it. For most news publishers CMIS isn’t the answer.)