When editing an AGOL item details in HTML Mode, one can do all sorts of fancy HTML syntax yet not include the JS script that allows embedding of Google Analytics tracking code. Web content managers, for the most part, will not put media in a heavily visited web site that they can't track the effectiveness or feedback of what's being put in there. This includes web maps and apps produced by AGOL. Obviously allowing JS in the Item Details is a non-started, how about giving organizational account admins the ability to "turn on" google analytics for the whole org, then content owners can plug in their own GA tracking code in some field somewhere.
This idea has been merged with Google Analytics tracking for ArcGIS.com items?.