Why is it that it took Egypt this long to attack these places? If they have known about the weapon storage why wait till 20 soldiers are killed. Why not hit them and keep hitting them. It's not like Egypt hasn't been fighting ISIS all this time

Probably a silly question but if these weapon storage areas and ISIS were known and where they were situated why on earth did the Egyptians not eradicate them prior to the loss of the lives of 20 soldiers.....???