It's not all that rare, and it's been there since day 1 for both systems. It used to only show up on skirmish or rumble playlists, but was recently added to the control playlist. I'm not sure how they set up map selection, but sometimes you just don't see some of the maps at all. I don't think I've played the first light map in about a month, though I really don't do crucible all that often so that's part of the reason.