Certain plugins are activated upon upgrade but in some cases these plugins can be activated automatically when another plugin is activated due to dependency. This article details the steps on how to find out how certain plugins are activated automatically.
1) Have the name of the plugin in question (i.e. we'd like to determine why Connect Support plugin got activated automatically)
2) Navigate to System Definition > Plugins (v_plugin.list)
3) Expand the filter breadcrumb and search for Requires contains "Connect Support" (or the target plugin)
4) The result will display the plugins that would automatically activate "Connect Support" if they are activated