I wrote my own CMS, as the core WordPress functionality wasn't too much to replicate.
But eventually the WordPress ecosystem was too strong, and the real value proposition was plugins and familiarity. That continues to be true to this day, which is why no CMS has de-throned WordPress in spite of significantly better UX, architecture and developer experience. None of it matters when the client has a suite of plugins they have been using for 10+ years, that are now core to their business.