I can’t alter the ‘entity.media.route’

I want my drupal user to see the media edit form using the frontend-theme, not the admin-theme.
In my RouteSubscriber I use
if ($route = $collection->get('entity.media.edit_form')) { $route->setOption('_admin_route', FALSE); }
The function works for ‘book’ entities (for example) but not for media.
Did somebody already had this problem?