Motorcycle windscreens, made of plastic cant be scrubbed as scrubbing scratches the plastic. to remove the bugs.
Bug Off and RainX are good products that not only make bug gut removal easier, also sheet rain water off like a waxed surface
M/Cs dont have wipers. So applying a release agent is best for them , not feasable for most.
Scrubbing off glass is a little more work and $ 0cost than treating with a release agent to get the bug guts off.
M/C yes. Glass no.