Because bombs are awesome. They can stun, kill, distract and cause irreparable mayhem!
In this latest video from Ubisoft though, it appears that we will not have to take bombs with us when time traveling at all, because the great and glorious Assassins already have them. All hail EZIO!
It seems as though every time the Assassins Creed franchise seems to be out of ideas, the developers add something new, and bombs are about the coolest thing of all.