I suppose I may be partly to blame, lol..
I have noticed a major increase in vintage items for sale, mainly because as others have mentioned, a great deal of older people are passing away or going into retirement homes / downsizing. This means most of their goods tend to be sold at estate sales by their children and/or heirs, who have sorted through them, rescued what items they wish to keep, and are selling the rest.
While I often see items that I cannot beleive they are parting with, I can understand, as one cannot keep everything, and though they probably have modern style homes, who knows? Maybe they are selling Mom's Frigidaire Flair because they kept Gramma's Hotpoint. Maybe they are parting with Gramma's sewing machine because they kept Great Aunt Emma's. Or maybe their Mother-In-Law was so awful they wouldn't let a thing from her home enter theirs, (I actually was told this was the exact reason for a sale by the daughter in law a few years ago).
Either way, I try not to judge people for why they happen to be selling items. Especially since while I am shopping for myself, I usually manage to pick up at least a few vintage items, that although they are not things I collect, they can be re-sold on ebay to generate a bit of income for myself.
I look at it this way, from what auction agents have explained to me, (most local estate sales are auction type), items which do not sell are generally thrown out at the end of the day, as the heirs do not want them. Some actually have a truck waiting for just that reason. So by purchasing items which don't interest me or others, (I dont buy expensive items, as I cannot afford to be part of a bidding war), and re-selling them, I am sending them on to someone who does want them, rather than letting them go in a landfill. I don't expect to ever get rich this way, but doing so helps to offset the money I spend on the items I do collect.