“burakumin” sounds a bit like the Indian untouchables who also worked with unclean things including body waste.
Since the Samurai worked with fresh kills, they would not be exposed to the same germ problems that workers with longer dead animals and people might be exposed to. Possibly it was a public health issue based on bad illness experiences with those who handled rotting flesh and hides. Of course, they didn’t know about germs in those days.