After the death of Ben Tennyson, the omnitrix was held under extreme, stern, and global lock down. No person alive knew where said watch was held, but of course when Vilgax discovered this (still sucked and trapped in the Void) he sent out his millions of loyal alien servants to do his biding and find the omnitrix. His minions have destroyed, killed, and left behind hundreds of planets. Their next destination to look? Earth.
It is up to you to either protect Earth, help destroy it, or go looking for the omnitrix yourself for good or bad.
It is up to you to either protect Earth, help destroy it, or go looking for the omnitrix yourself for good or bad.