Because Megatron can do what he can't, and he hates it. Because he can't protect his crew, can't protect Drift, from Tarn but Megatron can. It's his responsibility, and there's some satisfaction to be had in the fact that Megatron acknowledged that much. But it still leaves him robbed of a chance to prove that he's learned his lesson, that he's capable of being better and doing better and-- he curls in on himself further, optics flicking up to meet Drift's.

"You didn't even tell me to leave," Rodimus protests. At least he should have been able to do that, but it was Ratchet who kicked him out before he'd even had a chance to say anything. "So I just thought--"

He's a giant baby, is what.