Buddhism has no congregation in the Abrahamic sense and no obligatory weekly assembly, which is why census numbers for it are so unreliable. The unit is a place: a monastery you visit to make offerings, a village temple that handles funerals and blessings and stores the community's memory, or, in the West, a rented room with cushions and a Wednesday evening sit. You attend without joining. There is generally no register, no confirmation, and nothing to leave. The exceptions are instructive — Soka Gakkai and some Japanese schools do have formal membership, and they are also the ones that grew fastest in the twentieth century.