Supply = some dupe wave came up and I missed it ?
Demand = ?
Pre warlock, there was a steady supply and a steady demand. Relatively balanced market, with very few minor flactuations.
Warlock drops, and the game got a new life. Players who had quit came back, game is being pushed a lot more on media and social platforms, and you get more new players.
So, you have a steady supply that is now overwhelmed by the infux of new and returning players. More demand on a "fixed" supply, means prices go up.