When they do, the wild horse lovers, of which there are many, many, many in the US, complain that BLM is being cruel. Then after the round-up, the grazers complain because BLM didn't catch all the horses.
After the round-up, they have to store them. They can't kill them or sell them to processors. They have many huge pens where they store these horses that they have to feed and provide vet services until natural death. They probably have more horses in these pens than there are on the range. They probably spend more money on these stored horses than they do managing the horses on the range.
Yeah, that's what the article said. More good intentions gone wrong.