First, I don’t accept that it can’t work, there are still holders of power in Haitian society, and if you get them to negotiate and agree to a peace then it will happen.
But even more importantly, having order imposed by force by hostile foreign governments is no more guaranteed to improve the lives of Haitians, and it could make things much, much worse. A real solution for Haiti needs to come from and be supported by the people. We’ve had a series of US imposed foreign puppets for about a century, and the current situation is the direct result of this failed policy. This medicine is already killing the patient, applying more won’t help.