Ever tried to sell a used PC? Not saying it should be, but they devalue in price so fast it's nuts.
I see reasonable laptops on ebay for << $100. May as well keep a backup if that price (minus shipping expense and other fees) is all you're gonna get.
Maybe those few who do sell and those few buying them super cheap (I have my eye on a Dell i-3 laptop machine priced at $20 w/o a drive - half the price of a raspberry pi, but with a keyboard, and display) are why there are fewer new sales - maybe the Brits are smart! And this would also account for flash sales not tanking as badly as well.
A lot of this is like stock market pundits. Every single day if there is movement, they have to come up with a "because" - which is often whatever would most confirm their audience' confirmation biases, and which certainly has little to no connection to facts (else they'll all be too rich from trading to bother with talking in a studio). It's the same argument as "why don't psychics always win the lotteries".