The horse populations in the two herd management areas on the Western Slope have exceeded the number of animals the BLM believes the range can support. This summer’s extreme drought has shriveled grasses and dried water sources, amplifying the need to move horses, said Tyrell Turner, the BLM’s Colorado northwest district wild horse specialist.
[...]
An estimated 1,145 horses were living in the area before the roundup — significantly more than the 135 to 235 horses the BLM believes the land can support.
[...]
“There are heated debates around gathers and activists trying to stop gathers,” Day said. “And maybe they need to spend some time on the range and see horses that don’t have any water and are thirsting and starving to death. It is not a pretty death.”

It does sound like there's some justification for doing the job quickly. The population seems to be drastically out of control. This operation...

During a helicopter roundup, a pilot flies a helicopter close to the ground to push the horses toward a corral, sometimes for miles.

...sounds like a dangerous thing to do. I can't really blame a contractor pilot for not wanting passengers along.

... some areas, like the Piceance-East Douglas, will likely continue to require helicopter gathers because of the size of the management area and the rugged nature of the terrain, Turner said.

It sounds like a situation with no good answer, really. The article didn't quote any practical alternatives for reducing the herd size in the short term.