recently Adobe has deprecated the Adobe Extensions Manager in favor of the Adobe CC Desktop app. With CC 2015, Adobe has changed the way Extensions are distributed. Now they want customers to install Extensions using their Add-ons website: https://creative.adobe.com/addons
and, after installation from the above website, the Extensions automatically show up on a customer’s Adobe CC Desktop App.
Quark has submitted its App Studio Exporter Extension plug-in for InDesign for approval on the Adobe store and hopefully Adobe will approve it soon. Then it will be available through Adobe’s recommended, standard process.
In case somebody needs an immediate solution, we can help provide steps to doing a manual install of the Extension for CC 2015.