Existing religions have inertia. Parents naturally indoctrinate their children, and certain religions like Christianity expend lots of resources to convert non-

Existing religions have inertia. Parents naturally indoctrinate their children, and certain religions like Christianity expend lots of resources to convert non-believers (missionaries, community outreach, etc.). Religions have the ability to adapt, through reform movements, to better match modern values. It's also very tough for new religions, as they often rely on claims of miracles. Nowadays with cameras etc. it's hard to believe anyone's claims of miracles. Even Christians are often skeptical when another Christian claims that some miracle occurred in the modern day.