Many things, but first and foremost: the yoga community is a unique crowd, partly because of their diversity (ranging from hippies seeking enlightenment in remote Ashrams to high powered executives that use yoga to de-stress during lunch), and partly because of its general distrust of business and corporations.
The yoga market is peculiar because it’s grown to become a $20B/year industry in a world where words like “money” and “profit” can be dirty words, due to the spiritual and holistic lifestyle aspects that are associated with yoga. We've been very careful to appeal to the entire spectrum of yogis, and YogaTrail has been very well received to date.
Secondly: yoga professionals are organised into a vast network of independent operators (the teachers) who are loosely attached to studios (local) and yoga retreats (exotic and far away). Our site and database structure is built around that idea, and we have viral invite loops that exploit this social landscape.
Thirdly: community-based directories are a lot of work.