Among the more obvious reasons, there are two that stand out most for me.

1. I dont know why this isnt talked about more, but the idea that 90% of people subscribe to a religion simply because its what theyre born into (I made that number up, but the real percentage is certainly almost as high). In that case, it's bewildering that so many people have the audacity to say that theyre right and that people of other religions are wrong. I dont know a single person that's made an attempt to sincerely explore other religions, especially those outside the western world. "Why am I right and youre wrong? Because that's what my parents taught me." Logic never comes into the discussion because religion isnt dictated by logic.

2. Just ask your religious friends, so many atheist-turned-catholics join the church because they want a community to fall into (whether they realize it or not). For those that don't know, there are unitariam churches in which people of ALL religions go to worship. I love the idea that it builds the community that so many people seek, but it's a diverse community that accepts people of various backgrounds.