The only reason Wordpress and Drupal became successful is because PHP is present on basically every shared host you can find on the internet. They stayed successful by building a community of plugins and themes.

The actual internals of both are a complete mess, and trying to get them to do anything outside of trivial blog hosting and content management is a nightmare.

Just because you don't know of any Python/Ruby/Java "apps" doesn't mean they don't exist. Jenkins, Redmine, Trac, etc.