Why did WWE not have Angle face Undertaker?

It would have been perfect fit for Angle to face Undertaker at WrestleMania 22, But instead they had the match at No Mercy and then Taker went on to face Henry at WM. Taker vs Angle would have been ten times better. Randy Orton could have won the World title from Angle at No Mercy then lost it to Mysterio at WM