It may be, that one measure of the popularity, or not, of 26" barrels, is to look at what is being offered on new guns.
As I peruse the internet sites, I find few new 26" field doubles. most are 28". That includes over/unders as well as SxS. Target shotguns are obviously excluded as it's virtually impossible to find a new quality target shotgun with 26" tubes.
Truly an unscientific view on my part, but an observation nevertheless.