It's wild, isn't it? The situation is that Marauders (like, the "Harry's parents" generation) has taken over fandom for various reasons (I believe the relative lack of source material about that generation is one of the reasons; those characters are considered by some to be less tied to JKR), with Sirius/Remus becoming the top M/M ship.

Dorcas and Marlene are two witches of that generation, and I suspect they are primarily a secondary ship, though I've read decent fic where they were the top-line pairing.