Just curious - how do these companies do that?
Most brush makers do not sterilize the brushes. I believe Simpsons do sterilize them. If you are referring to barbers. I'd read of a barbershop that sterilize with Barbicide. The best cleanest sterilization process that I know of, autoclaving, cannot be done on brushes. The autoclave will practically melt the glue that's holding the brush together.
I don't trust that even if it says sterilized. Everything gets a dunk in the barbicide before it hits the face or hone. I think disinfect is a better word. Sterilization would mean an autoclave or vigorous boiling or steam.