There is something called "Updates" in software development, where a developer can release an initial version of the software and update it when needed.
I hope this is sarcasm.
Sure, he could have released the exploit at christmas, but I think the current popular excuse is that he was trying to find out some kind of safeguard so that less people would brick their consone when trying to apply the exploit, so really he was just looking out for the wellbeing of the community!