Considering that the competition are ROTF and AOE, that's not hard.
Cos space is freakin' massive and he most likely ran out of fuel by the time he exited our solar system (let alone galaxy). My initial thoughts was, "Well that was stupid idea, wasn't it?"It's incredible that he even had enough fuel to escape Earth's gravity and make it into orbit, let alone embark on a long space voyage. Transformers have previously been shown to use spacecraft to travel between worlds such as the Ark, the Nemesis (where The Fallen was seen), the Xanthium etc. Only those with jet modes like Megatron and Starscream seem to have the ability of achieving and sustaining interstellar flight, and they can only do this in their alt modes.