Why do Christians continually try to convert Atheists?

You have to admit that if a person was let alone to their own thoughts, they probably wouldn't be believers. They need the fellowship of other believer to help each other constantly keep up and reinforce the faith. SO they're always trying to recruit. I think it's the same reason drunks always try to get you to drink with them. If someone else is doing it, they don't feel as guilty or stupid or whatever.