Its because if you know the Transformer's story line you would know that the Decepticons are actually Cybertron's armed forces so they are all military other "tough" looking vehicles, in the cartoon they are also the only ones that can fly while in robot mode. The Autobots are basically a civilian militia who combat them after the Decepticon leader, Megatron, who was supposed to protect them go nutso.
"help im in a nutshell" , "how did i get into this nutshell"