I have been one of the maintainers of a moderately successful CMS back in the day, but there are definitely well-groomed alternatives that have popped up a lot more recently than that, especially from the headless variety.

I'm convinced the thing that WP did better was being the first simple and accessible blogging platform when blogging was still a thing. IIRC, the alternatives were things like Joomla or Drupal - awful behemoths for enterprise users. WordPress was a breath of fresh air compared to those, and out of the blogging scene, people started to use it for agency projects, while others published an ever-increasing number of plugins and themes. The rest is just momentum of that movement.