Lack of exposure is the popular answer, and my answer as well, although I guess it's been disproven by the powers that be.
I have trouble with Steppenwolf's example above, since I've seen somewhat regularly on auctions after they close, more than one person lamenting that they missed it. For whatever reason, it would appear that now more than before, people are missing auctions.
As someone who has won probably 30-40 auctions in my short time here (and probably more involved than anyone in non set auctions), I can share my take. I used to have fun doing auctions. Things came up for auction that you didn't normally see or for special reasons, and it was cool to be involved in that, whether gunning for something you could use or pitching towards a good cause. I won 5 of Kifers for his new custom set, 11 of Toby's 12 customs, random racks that weren't around at the time, great custom sets, full THC sets, oooo those Radissons.
(edit: to add to this, people ran auctions at $0 or low starting prices. I was picking up MAD shit when I joined via auction, it was a blast. And guess what, those were resold at the SAME price. It was slow and dry at that time. Now? Prices are jacked, everyone's digging for pennies, and auctions are starting towards top pricing, because why would you let it go cheap?)
Now? You have people that auction off their 20 starbursts, and their 40 roulettes, and their 100 mermaids, and normal everyday nonsense. Or you have others that run auctions regularly for a week or 10 days. And then bump every day with literally no other involvement.
Do we need to find the "market value" on .20 a chip barrels? Do we need to so desperately ensure that every single person on the site over 2 weeks sees that one custom or one rack that isn't that rare?
Everyone can think what they want, but it's pretty obvious. So, to those people who need to auction every single sale, or run them for weeks, have a great time. Too bad auctions are poo poo for awhile, maybe they'll be fun again soon.
(I don't care how people sell, I love everyone equal, their chips their decision. Just connecting people's decision making and how it's obviously connected to OPs topic.)