I think, in a parallel of canon, Itachi did “spare” Sasuke from the entirety of the curse. So, since in this AU he put the entire kingdom to sleep instead of killing everyone, Sasuke’s sleep curse is probably a partial thing with a set of conditionals to break it or something like that? So it was weaker to begin with and he broke it himself because of Vengeance.
But, as you said, there is the trauma side of it which probably causes him to avoid sleeping in exchange for obsessive training. Or just really persistent insomnia.