Given the amount of time it took to get from the irken empire to 'earth' you suspected the tallests really wanted Zim as far away from them as possible. Now why go to earth? Cause you knew you wouldn't be found there. You see you had a history of.. well. Mutiny. You've been on the run for about 3 years now, what did you do? Oh ya know nothing much just decided to commit mass genocide of your own people. You were feared by your kind. Why did you do it..? Well...That's a story for another time. You smirked as you entered Earths atmosphere. This, was going to be fun.