Why do I need to enable the Drupal Bootstrap theme when using a Bootstrap subtheme? I'm trying to learn how to use the Drupal Bootstrap theme to create my own subtheme.  I've added the Bootstrap theme to my drupal/themes directory, and chosen SASS as my sub-theme starterkit (i.e. I've copied drupal/themes/bootstrap/starterkits/sass to drupal/themes/mynewtheme).

I understand the concept of how sub-themes work: the sub-theme inherits the parent theme's resources.  But I don't understand how it works in the case of the Drupal Bootstrap theme.  Once I install the bootstrap framework into my sub-theme (per the instructions on the Drupal Bootstrap sub-theming instructions page), what resources is the sub-theme inheriting from the main theme?
I do not why, but bootstrap sub-theme requires bootstrap theme also enableled in order to inherit all settings, in D7 theme and sub-theme must be to be in sites/all/themes folder, D8 theme and sub-theme in /themes folder, just do it and all will work fine.