Supply and demand, yes.
My personal observation is that late model used 16'ers command a higher price than late model used 13'ers, but as you move into older and vintage units, the differential decreases and eventually favors the 13'ers. The smaller ones seem to be in greater demand as restoration projects. Kinda makes sense. A smaller, simpler trailer makes a more manageable project, and there's a "cute" factor as well.
There's a similar pattern in used Airstreams and vintage stick-and-tin trailers.
Scamp has consistently
sold more 13'ers than 16'ers over the years, and not by a small margin, maybe like 2:1. The pandemic may have given the 13'ers an added boost as people pivot to RV travel and want to use smaller vehicles they already own, avoiding the seriously out-of-whack vehicle market.