[Well isn't that a loaded question. Sasuke can't say he's at all surprised to hear it though.]

Many reasons. The short form is that you and the previous three Hokage were all resurrected with the Edo Tensei. So was my brother.

[A beat. Sasuke frowns at nothing for a moment.]

I don't like this thing we call shinobi. What it entails. How many people it hurts. But destroying the people also called shinobi won't fix it. [The slightest pause.] Won't bring back my clan.

Instead I'm going to fix the problem, and stop more people from being hurt like I was.