Not sure if it was discussed but this is the whole explanation. and... it really has blew my mind O:
It makes perfect sense! Why else would the Thalmor invade Skyrim! I wouldn't be surprised if they'll also try to get their hands (if they didn't already) on an Elder Scrolls, go to that point where Numidium was activated, and do something there to destroy it too so the world would end :S
What do you think?