Reply To: the_ID = 0
The id is zero due to the way BP constructs those pages.
The how and why is a long answer – you may want to look at the codebase to see the how.
In any event, you will not be able to change that.
Your best bet is to add to the display conditions the user has set.
Perhaps…
Give them an option to select the Groups Directory page.
Then use bp_is_groups_directory() to check if they are on that page.
Or maybe specific single groups.
Then check to see if they are on a single group page by using groups_get_current_group().
So the basic approach is to use template tags to find out where the user is and then show or not show an ad based on the the display conditions the user has set.