Hmm, Well from what I can remember, all pushback skills are diabled in Woe.
Also - I think that when you get hit by Stormgust, a Sin usually slows down while taking damage, right?
With backslide (Correct my if I'm wrong) You'd be able to get through a SG extremely easily, and quickly. (wearing Marc)
Again with the ninja Skill Hidden water, You'd be able to bypass that as well.
Basically, thats the only reason I can think of, that it would be disabled