Board Thread:Questions and Answers/@comment-25959945-20170718204052/@comment-1038387-20170719092851

They didn't "forget", this is just how they chose to adapt the Flash. There is no Speed Force in Young Justice, so their powers work differently.

And the only shattered knee I can think of was Bart Allen, in 2004's Teen Titans ½. His powers work differently from Wally's anyway.