Traffic experts have been telling politicians for years that you slow traffic not by slapping up speed limit signs and ticketing drivers, but by building physical and visual barriers (narrower streets, speed bumps, narrowed intersections, etc.) that force drivers to slow down. It's not like our government does not understand this.
It's just so much easier and cheaper to get political points by championing a helmet law. I make my kids wear helmets when they ride their bikes. Far more important, I teach my kids how to ride defensively to avoid being hit by a car. This is the responsibility of parents, and we, not politicians or cops, are best placed to do it.