It's openness to some different cultures helped it spread widely in places like India where the more traditional strains of Islam butted up against things like the local integration of dance with religion.
I should expand on Aslan's point also. He thinks that if not for the Sufis, then the inherent Muslim antipathy towards various "polytheism," "ritual dance" etc. would have prevented the spread amongst the common people of India overall. That might have made for some different history.
