My guess would be because 'designed for' commuters are expensive and many folks do not even know they exist. In the 50's and 60's I rode 3-speeds, in the 70's and 80's road bikes, in the 90's I bought a mid range cross-bike and converted into a serious commuter, that even today the only real change I would make to it is an 8-speed internal hub instead of the derailler system and replace the lighting system which was never really satisfactory and has been abandoned . However, I do not need a commuter any longer. I could ride it into town only I am philosophically opposed to their helmet law, what I get for moving out into the boonies.