The BLM does it to mark the horses as U.S. BLM property, no owner can change it. It's also a freeze brand, it just kills the hair on it to make the mark and doesn't hurt them.
Rick Bradley freezing isn't painless. and these horses have it really all over them. does it really have to be that much of this brending? or just BLM don't give a crap about horses, as ususlly?
What they want is to keep the horse population in balance with the environmental resources which they easily overrun. It's a difficult problem since horses are very adaptable. Investigate the Brumby horses of Australia to see how destructive over population is to where all the horses suffer thirst and starvation and slow death because of their numbers. No one wants to get rid of these wild and feral horses except cattlemen wanting the take those resources for their cattle. Blame them and all the people who buy and consume beef.