Let me simplify my question then.
Why would a disbeliever study religion?
I dont think there are many disbelievers who study religion but only that those who study religion show up more in similar forums.
All the reason people have extra information that has no practical usage serves to one end that is the power of having information. Thats one reason. They just like themselves better that way. which is fine because many religious do the same to religious information as well.
The other reason can be perceived humanitarian in a way. They usually come from a strict religious background, feel themselves relieved after their giving up on religion and want others to feel that way, too. But this is a false belief to think you can help each and every believer that way since it is destined to be a hunger that can never be fulfilled. You cant help everyone on earth through your calling and this is never your duty unless you received a call from god directly to do so
The main reason, the religion and their connection to god is always there. It is an endless search that remains there untill it is begun to be fulfilled the right way. It is everywhere they look.They just want to deny it by fighting with others through their knowledge. the more they feel beaten the more they want to learn, the more they win the more they want to learn. They spend their all lives learning about the religion like a priest but not for the main purpose which is fine also because most religious people do the same,too.
So when they die eventually most priests will have a lot to talk with atheists in heaven.