They claim it is for national security purposes, which could be to help prevent remote-controlled bombs or catch people sending LM messages over the Internet. But I think it is just increasing control over the population in general.
I assume it's to track any sim back to the owner if it gets used in a phone to remotely detonate a bomb. Or by spy agencies listening to conversations. Australia has the same deal, you have to give passport or driving license details to activate a new sim.