Because, you see, Ygerna wants to be resurrected. Damian wants Ygerna resurrected, although he doesn’t know he does.
What a b***it. From the start of the game - that was the whole Damian's plot. He acted like he doesn't (pretty obvious, because resurrecting means death for Damian since he inverted the Sould Forge spell; this, actually, a lie spread by Damian itself, I believe) because he wanted to make Dragon Knight (protagonist) and Zandalor do the job (the Damian itself wasn't the dragon descendant so he wasn't able to do some things) for him. As we can see in the end-cutscene he is not surprised (not even a little) that Ygrena has awoke, because he waited for it since his plan succeeded. How in the hell these "reviewers" come to such incorrect conclusion - hard to imagine for me.