Guilt isn't an emotion Sentinel is even remotely close to being capable of feeling. Hell, he's not even regretting things the way he should. His main thought is, why didn't I kill everyone?

"It's hardly on your shoulders," he starts. It's easy to brush it off when he can't empathize himself. "The system was designed to restrict and prevent anything from being done. When something was..."

Then Sentinel was called in to make that something disappear. He's not sure where he's going with this but he knows it's important Optimus thinks he actually gives a fuck. Fake it 'til you make it, right?