Why does he keep this up?
It goes against what is taught in the Bible (i.e. Matthew 24), he knows that nobody will believe him now that he's been wrong twice with his past "Prophecies," and he is an embarassment to the Christian faith as a whole, as many unbelievers think that all Christians worldwide agree with what he is saying (i.e. check out pretty much any DU thread relating to his Rapture prediction and you'll see what I mean), and this will worsen when things don't happen the way he claims in October.