Optimus seems withdrawn, cuz Optimus is a wuss...
Here's why (if that world were real):
They come to earth. They "defend" humans from bad-azz crap from outer space. They form an "alliance" with the U.S. Army, yet when sh*t hits the fan, the Army is rather useless. WTF? WHY? (I guess it's an insurance company thing, so they can deny claims because of the U.S. military involvement they can cite "act of war", etc.)
What's in it for the Autobots? Plus, when they fight, half the cities are destroyed. Nobody seems to care how many humans die in the process. Anyone see any Autobots attending their funerals? Then in this trailer, he's P.O.ed apparently at humans. Why not just smash the people causing the issues and be off to another planet?
Optimus could litterally say "F.U. humans. We're taking the planet. Nothing you can do about it." But he doesn't. Cuz he's a wuss.
Ok, I'm just joking around. It's just a movie for pure entertainment. Just pointing out how silly the whole premise of these Michael Bay movies are. Kinda like those Fast & Furious movies.