First of all because you do not need it- the fairing screws attach to a rubber plug with a brass insert inside. When the fastener is tightened, the rubber plug squeezes against the fairing and maintains force against the screw so it cannot loosen. Also those screws are very well isolated from any vibration.
A few folks have used a thread locking agent on fairing screws with disastrous results; I think it was Haroldo who had a bunch of fairing screws that he just could not remove because the screw was locked to the brass insert and that was spinning inside the rubber plug.
I have seen a lot more damage done by using thread locking agents than cause by the lack of them. If fasteners are correctly tightened they are usually not needed. Occasionally there is a sheet metal nut or some other type of really light duty thread retaining device that just will not allow a fastener to be tightened enough but these are not usually found on motorcycles.
Brian
Just out of curiosity, why not? There are compounds, such as Loctite 242 that is designed for use on fasteners that require removal, with hand tools, for normal servicing??