In my experience, people primarily leave for two reasons.
First, people realize this is a moderated forum and they can't get away with abusive behavior or preaching/proselytizing. They are used to forums that aren't moderated where they can say whatever they please without consequence.
Second, people leave because they take things personally. They take someone challenging their beliefs as a personal attack and become upset when people don't agree with what they believe.
While I'm sure there are other reasons, in my experience, these are the most common.
First, people realize this is a moderated forum and they can't get away with abusive behavior or preaching/proselytizing. They are used to forums that aren't moderated where they can say whatever they please without consequence.
Second, people leave because they take things personally. They take someone challenging their beliefs as a personal attack and become upset when people don't agree with what they believe.
While I'm sure there are other reasons, in my experience, these are the most common.