I don't really see this mentioned by anyone, but mobility is also a big factor. There are a lot of people who no longer live anywhere near where they grew up or where their parents or extended family live now. Great solid furniture (or anything 2+ states away from your home) is expensive to move. My parents may have a great desk that I'd love to have someday - but probably not if it means I have to arrange to ship it from Arizona to Chicago and wonder if it's still going to be so great after the stresses of moving. I still have some of the things they left behind when they moved like the head and foot boards for my childhood bed - taking up space in the garage, maybe to be useful if having kids had been part of my lot in life. As it is, they'll end up in the trash when I get around to cleaning the garage or move.

A lot of the place in the world for family heirlooms went the way of the family homestead.