Is antiquity + numbers.

Lamaism has been around since the 7th century and is the indigenous creed of a large country. Scientology is less than a century old and is limited to a few Hollywood kooks.

And Lamaism, a quaint term that’s not in fashion any more, should be revived because it’s more accurate than Tibetan Buddhism. It’s a fusion of Buddhism and tribal shamanism, and quite distinct from the more pure Mahayana and Theravada mainstream. Real Buddhists don’t believe in an anthropomorphic God and certainly not an earthly incarnation of a god.