From the mid 80s to early 90s, comic collecting was huge. But for some reason that scene went bust. I would assume that truly rare, vintage comics are still valuable, but what's the use of collecting new comics, when so many others are doing the same? If tons of particular issues are being preserved, they'll never truly be rare, and thus won't ever be worth much. It's the difference between old, commonplace stuff that gets sold off cheap, and exceptional, uncommon antiques.