From the Gatsby blog on their choice to use headless WordPress for their blog:
The Gatsby blog has content from 133 authors. We’ve published articles from our community, technology partners, and staff members. WordPress enables us to have unlimited users (without paying a subscription per seat). WordPress also comes with powerful role-based permissions and has free plugins from services like Auth0 to unlock flexible security and authentication options. Those features made WordPress a perfect fit for our particular use case.