IMHO, the popularity of the O/U is also a generational issue, as the SXS lost it's popularity after WWI, in no small part due to it's higher cost. After that, young gunners were raised on less expensive single barrel guns like pumps etc. Moving up to an O/U provides the same type sighting picture as opposed to a SXS, which can take a little getting used to.

Regards
Ken

I prefer wood to plastic, leather to nylon, waxed cotton to Gore-Tex, and split bamboo to graphite.