01 Feb '14 13:57>1 edit
Consider your question amended; why do so many avowed theists come here to argue about their faith, since they already know the true nature of reality?
I'll tell you why I post.
Because of the sheer joy of sowing seeds of truth which may one day result in someone meeting Jesus. That is just like one day each of us believers in Christ did.
You call that proselytizing. Jesus called it going into all the world and preaching the gospel to every creature under heaven.
I know I may not witness the changing of a life once it has met Jesus. These things do take time. But there is hardly any higher joy then leading someone to meet the Lord Jesus.
If others look at that and say "Aha, you just want proselytes" so be it.