A friend of mine and I grew up collecting together. Later I moved away for college and work. He has a raw Hulk 1 in about 5.0 and an X-Men 1 in about the same condition. The X-Men cost him $150 in the mid-80s. Has some nice early Spideys but no AF 15. He has a sizeable collection, but long ago he moved on to collecting movie posters and autographs. He's heavy into horror movie memorabilia and makes costumes.
He is very attached to his stuff and he would never sell any of it. Maybe on his deathbed. None of his comics are graded, none have ever been scanned, none have been shared on the Internet. He doesn't care for online groups and forums. He isn't swayed by talk of money. He doesn't check GPA every week on the value of his keys, although he might flip through Overstreet every couple of years.
If I know one guy like that, how many others must there be of the 320 million people in this country? I don't tend to think of the original owners who might still own their copies, but the thousands of collectors who may have picked up these books in the 70s, 80s and 90s and who have them out of sight, out of mind, and are busy with other aspects of life.
Remember before 15 years ago, there were 0 CGC-graded copies of AF 15. Now there are X amount. 15 years is not a long time. Do you expect everyone to jump because someone down in Florida starts gluing comics inside hard plastic?
Somebody mentioned they couldn't understand a person not being tempted to sell belongings if they were worth several thousand dollars. It's very easy for me to understand. Happens all the time - think family heirlooms. A lot of people really are just fine where they are.