People genuinely want starters with provenance. Some cultures have documented lineages going back generations, and bakers ship them across countries. An exchange would be charming and entirely practical. The starter is the living culture that makes sourdough work, and the community around it is unusually devoted. People name theirs and maintain them for decades. The market underneath is real: cultures, flour, banneton baskets, dutch ovens, scoring tools, courses and books, selling into a hobby that grew enormously and then stayed.