Way back when, in the early days of CiviCRM, there were two CMS’s supported, Drupal and Joomla, and CiviCRM’s codebase was complicated, but ran reasonably well. After a few years, the code was greatly improved but also significantly expanded to include a tremendous amount of additional functionality, and thus CiviCRM became a serious server resource hog. Finding hosting that could run it at all was sometimes a challenge and finding a host that could run it well was difficult.
I know... CiviCRM for Professional Organizations and licensure. What a thrill ride! Bear with me and hopefully this will be an interesting read.