There are a number of possible reasons that the typical LBS does not stock hub generator lights and friction/rim generator lights. They are rather expensive, and many "weight conscious" consumers would notice the weight.

Today, modern lighting systems are becoming lighter, brighter, and less expensive.

One of my favorite "around the neighborhood" lights is Sigma Cubelight LED headlight. An LED light does not have a bulb that will burn out at the worst possible moment. The Cubelight uses a "click down" clamp that lets me move it from one bike to another in under thirty seconds. It uses five AA batteries. I use 2500 mAH NiMH rechargables that provide four or five hours of bright light per charge.

Sigma sells a $15 "egg" sized charger that plugs directly into the light, and fully recharges the batteries in about eight hours. Those batteries are good for at least 500 charge/re-charge cycles, so I will get a couple years of use from them. That reduces the operating cost of the light to pennies per night.

I use the Cubelight along with a Sigma TriLED strobe light. That light blasts a dazzingly bright strobe light into the eyes of on-coming drivers to wake them up. A set of three batteries lasts over a hundred hours. The combination of the Cubelight, to light the pavement, and the TriLED to alert motorists, works very well, and costs less and weighs less than a typical generator-style lighting system.