> I will just build an admin dashboard that allows a site owner manage their content
With WordPress, there are 5 different plugins already built that have more features than the dashboard you're planning to build, and the agency/person maintaining the site may already be familiar with them. WordPress and other PHP CMSes may not have the best architectures (Drupal was downright atrocious), but the ecosystem is thriving with pre-built, customizable tools for the 99% of customer needs.
Virtually all web hosts, including very cheap ones support PHP-cgi and MySQL, so deploying WordPress is frictionless. CMSes written in other languages have deployment more friction.
With WordPress, there are 5 different plugins already built that have more features than the dashboard you're planning to build, and the agency/person maintaining the site may already be familiar with them. WordPress and other PHP CMSes may not have the best architectures (Drupal was downright atrocious), but the ecosystem is thriving with pre-built, customizable tools for the 99% of customer needs.
Virtually all web hosts, including very cheap ones support PHP-cgi and MySQL, so deploying WordPress is frictionless. CMSes written in other languages have deployment more friction.