Usually in Content Management Systems like WordPress or Drupal, the admin area is something permanent. It exists along with the public part of the site. But imagine that you have the site admin area only when you need to make changes on the site. This way, it doesn't take hosting space and resources and doesn't require it to be up to date to avoid vulnerabilities. Let me show you one example, it’s my personal Drupal 9 site https://abzats.com/. It’s built with a Tome static site generator (https://tome.fyi/).