Why not? I can only guess it might be because it would cost Strydur twice as much [money, time, aggravation] to keep DOUBLE the inventory of two sizes of every one of dozens of MHS parts "in stock"? Or maybe he could just discontinue half the parts he makes now and/or take twice as long getting them back in when something goes "out of stock"? I bet we'd all be real happy about either/both of those options eh? ;)
I have small hands myself but really the MHS parts are not exactly uncomfortably "big" compared to certain MR sabers and iirc the rationale behind the 1.45" MHS standard O.D. was so that one could fit a 1.25" PVC pipe inside for chassis and a 1.5" sinktube outside for overlays which alloys a lot of versatility for the 'fancy' designs so many of the great sabersmiths here make...smaller MHS parts wouldnt be able to use standard pipe/sinktube materials for chassis/overlays so I think that Strydur made a BRILLIANT inspired decision going with the MHS diameters that he did.
And for someone who has small hands really wants or thinks they need a small diameter for ease of spinning there are the choke pieces including the 'long' chokes which are really entire 'skinny' grips compatible with standard MHS pieces. I quite like them myself because of my small hands and would suggest anyone who thinks MHS is too 'big' in O.D. to give them a try...esp the long choke 3 which is fantastically comfy for small hands.