The auction house sucks and one of the ways it sucks is having to manually repost every single thing you want to sell every 48 hours. Someone would probably buy them eventually if you keep it up. I know I semi-routinely go look for obscure shit called for by some deck or other I've found on the boards and if I don't buy up a playset it's because not enough people are selling whatever it is. (or are posting a troll price, like when I was looking for Stingy Jack's Scarecrow Scythe equipment and the only two on the AH were pitched at 2,000,000 plat). But I would guess that set 1 has lower uptake overall between the sheer number of packs that were generated, the fact that it's going to rotate soon, and the more scattershot nature of the design. And it looks like most of the good cards from that set (Vampire King aside) have sufficiently exited the meta that they don't sell for much anymore. (Time for me to stock up!)
Drafting and evo gauntlet are the main PvP formats people play, I think, and you need to have unopened set 5 boosters for those or an equivalent amount of plat. (Or, come set 6, probably set 5 and 6). But I dunno, the selling point of the game is PvE, to me. And there's clearly a bunch of people playing that.