Originally Posted by Cult of Personality
When someone sees the Gate, Truth takes from them what they value most in exchange for the knowledge. There's nothing Ozai values more than himself.
Sure, but the thing is, Ed has no way of showing
the Gate to Ozai. Ozai can't even do alchemy. The only time someone has forced another to see the Gate was when Wrath and Pride forced Mustang through, and apparently that action strained them (at least, it strained Pride). Even then, they had to physically pin Mustang down. There's no indication that Ed could do the same to Ozai, and even if he did it would be irrelevant since if he pinned down Ozai he would have won already.