Power
Having power meant carrying an amount of responsibility equal to it. If you were unable to shoulder such a weight, then you would invariably lose you power; someone else would take it from you, one way or another. History had proven that countless times.
The abuse of power was met with forceful, even deadly, retaliation; that was why tyrants never could keep hold of their people for long.
There was no sentient life in the universe that preferred being controlled over having their own free will, and they would always, always fight back when someone attempted to take it from them.
That, Sam mused one rainy afternoon, was why Megatron and the Decepticons could never gain a solid footing over the Autobots and their human allies, despite their notable power.
Freedom was far too valuable to let the bad guys come out on top; and they were all willing to die to preserve that most basic right.