You said the same thing when I bought them lol. I think the Jack fracs are just a really unique combination - the fracs are so limited but the rest of the denoms are so plentiful that there are a lot of potential sets to fill.
In any case, as a recent beneficiary of the auction section, I'm certainly not one to poo-poo it, but I get why people do. Obviously, I think it has its place. There's just not a lot of Jack frac volume out there. I suppose I could have listed @ my purchase price in the classifieds, and then brought them down until somebody bit, but that's just basically just reverse auction. I didn't want to deal with the hassle so I threw them up for 3 days and felt like I got a fair price. For the rest of my Jack's set where prices are more stable, I put up a fair price and they sold. I'm not here to squeeze pennies out of anyone lol.
That said, after taking a ~1 year haitus from PCF, it's pretty clear to me that auctions in general are seeing less action than before. Less exposure from not being in the classifieds tab makes intuitive sense to me, but auction fatigue wouldn't surprise me either.