It's called item panic, pvp is nerfed, less gold coming in, kids need gold, goes back to regular activities (gwd,slayer), more of that items is coming from, which contributes to the less demand more supply, which makes for more selling, which causes a items crash. Also you can't forget about the panic sellers. But items like slayer drops, will stay above their start of artifact introduction cause there's still be the void to fill there.