The thread regarding the current doublegun collector's market got me thinking about where we came from.
As Mark observed there was little SxS interest (of course with exceptions like the M21 and British "Best") 50 years ago.
So what happened?

The first issue of the
Gray's Sporting Journal was 1975
Sporting Classics 1981
Shooting Sportsman was Winter 1987
Double Gun Journal was Winter 1989
I couldn't find when this Forum started but I believe shortly thereafter.

Double gun collector's groups: (please correct me if the dates are wrong)
PGCA 1993
Dr Bob's Lefever site about 1993?
LCSCA 2003
16gauge Society 2004
Fox 2006
Damascus Knowledge and Pete Mikalajunas' site were both in 2008, which I hope stimulated interest in damascus barrel SxSs, and possibly the value thereof
Daryl's Baker sites 2011

There are lots of gauge and SxS specific Facebook groups now

Parker Reproductions by Winchester were introduced late 1983

Bill Brophy's L.C. Smith book was released in 1977
Lefever: Guns of Lasting Fame 1986
Walt Snyder's Ithaca book 1991
McIntosh Fox book 1994
Semmer's Remington Double Shotguns 1996
The Parker Story 1997
Houchins' Smith book 2006

So the interest was generated, and through the ups and downs of the U.S. economy SxSs were purchased (at increasing prices) and used in increasing numbers.
I do believe, now that many of us are in our 60s & 70s, having "stuff" is less important than having (less) really nice stuff that we enjoy using, and collections are indeed being cleared out - sometimes by our survivors who have no interest (and sadly were left with little directions regarding value) in the guns. Many of us do have more disposable income after retirement and getting kids educated.

As said by several, the good stuff retains value, still sells, and IMHO will continue to do so. Well used 12g utility grade U.S. doubles are a hard sell, but decent condition small gauges are still sought.

The other dynamic however is that many of our doubles are now 120 years old, need repair or refurbishing, and the double gun expert smiths are fewer in number. I think that will be a major issue as time goes on.