From my perspective its because people won’t change their beliefs unless they stop benefiting the believer. For people who live in a religious community, there church’s sunday social event is enjoyable, there friends are all religious, there denomination provides a entire moral framework and worldview they don’t even need to think about. Confirmation bias plays a major role in preventing alternate thought to block out other worldviews.

Only when someone does not gain much benefit from there religion or has a important part of there religion proven wrong, can they process alternative ideologies and either switch to a more useful denomination or stop believing entirely.