The case for motorcycles. Why not use one?

[GasSavers_SD26]

Originally Posted by Mighty Mira

It's cheap for Honda to just modify their Cub for that purpose.

I think it's a cost issue with smaller bikes. You've got the actual fairing, then all the mounting bracketry. Mounting a simple fairing/windshield to the handle bars, a cheap, easy way to do it, rather than to the frame at the steering head also transmits any wind buffeting into the steering of the motorcycle.

Adding a fairing also adds weight.

Really, without a fairing, there's not a lot of frontal area on a bike. It's not smooth, but it's very small. I've seen race team test where they have gotten rid of the production full fairings and produced higher top speeds. Again, these aren't "dustbin" fairings to start with.