A lot of clients won't accept a custom CMS due to security concerns. Every line of code I write on the projects I mentioned before go for a security scan with a

A lot of clients won't accept a custom CMS due to security concerns. Every line of code I write on the projects I mentioned before go for a security scan with a third party. Scans already cost tens of thousands of dollars, using a custom backend would drive that price up even higher. In terms of PHP CMS's for enterprise, you're very limited, and a lot of companies are moving towards Drupal. The other major benefit is that it's (fairly) easy to swap out either the frontend or backend. If we need to migrate to another CMS, we don't have to change anything on the frontend as long as the new API confirms with the old. And vice versa for migrating to another frontend. Also if you need to create an app or any other application you already have an API. I wouldn't necessarily use this same architecture for smaller sites, but for enterprise it's a pretty good option.