The sad part of this equation is it's not that expensive to upgrade. My Caddy horns came from a Hearse that had burnt to the ground. They were about the only usable part left on the car. Two used horns, and a starter relay for a lawn tractor from NAPA (cost $10), and about 30 minutes work it's done.
Factory horns are "legal", so most people think they are adequate. "Legal" is a minimum standard thought up when everyone drove with their windows down. They may be legal, but all new motorcycles should have a newer standard applied. The way it is now, the larger the vehicle the louder the horn. In West Virginia a bicycle horn that uses a squeeze type air bulb is legal on a motorcycle. But that don't mean it's adequate.
"DUCK" WV