I guess it might be because of how traditional Hayate is in terms of outfits. Like if it's not ninja-themed, it has to look Japanese (even his Fighter pack looks ninja-themed).
For me, I just find it bland that it has to be blue when it could have been in a better color.
Well in DoA Dimensions he had a Tuxedo outfit and I don't say that it wasn't nice... but honestly I prefer much more a similar Japanese traditional one for him.
I think that Team Ninja don't give him Western casual outfits, very simple because it's exactly it to distinguish Hayate's look from Ein's one (of course, in this case I expect that they will give similar outfits to Ein).