tl;dr -- The longbow is worthless in most applications except military. The monarchy made it compulsory to train in bow use, so anyone recruited for the militia

tl;dr -- The longbow is worthless in most applications except military. The monarchy made it compulsory to train in bow use, so anyone recruited for the militia was ready in some shape or form to use the bow, so in a relatively short amount of time anyone can be trained to use a longbow for battle. They forced bow imports and kept prices very low throughout England. The rest of the world couldn't enact such rules and thus could not make the Longbow a successful military weapon. It required years of training, not something you can do to a soldier who just got conscripted.