Why Can't Panels Select My Organic Groups?
The way I accomplished this was with Views Contextual Filters and the Views Content Panes module, displaying only content belonging to the particular groups I wanted to see the content.  This approach, however, requires the content being viewed to have a field instance of the group ID that it belongs to (and, incidentally, a field instance for "other" groups the content will be visible in).  Note, in order for the two contextual filters to work properly here (i.e. for the content pane to be visible in two or more groups) I had to install the "Views Contextual Filters OR" module (I can't link twice because no rep).

I couldn't comment because I don't have enough rep, but this approach worked for me, but it might not work in your specific use case.  It should be noted that if nothing matches the filter, the pane is omitted from display entirely (which is what you are ostensibly trying to accomplish).  So many ways to skin a cat with Drupal.