Sailplanes capable of climbing in rising air (not troop transports, which can only descend after the towrope releases) have one or two seats. I know of only one type with more, the Schweizer SGS 2-32 "2​½ seater." Even experimental one-offs like the Perlan series have at most two seats.

Ignoring social aspects such as marketing, class associations, and racing leagues, what are the technical difficulties in making/flying/maintaining a sailplane with more than two seats? Frontal area, if seated abreast? CG range, if seated fore-aft? Something special about mass or wingspan that doesn't apply to powered airplanes?