What is a flat-file CMS? What are CMSs that aren't flat-file? How many CMSs are there now? How come people are still making more? Why isn't this a boring, fairly stable commodity category the way web servers or something are?
Probably too many [1].
> How come people are still making more?
To show they (or their new tech stack) can, to avoid licensing issues, or to have a system tied to their needs.
> Why isn't this a boring, fairly stable commodity category the way web servers or something are?
For what it's worth, it is... the market is uttery dominated by Wordpress (~43% of all websites, and 63% of all websites using a known CMS), followed by "WYSIWYG builder systems" (Shopify, Wix, Squarespace), Joomla and Drupal. The "large enterprise" market seems to be firmly in the hands of Adobe AEM which is an utter PITA.
[1] https://en.wikipedia.org/wiki/List_of_content_management_sys...