In the not-too-distant past, they were rounded up and made into dogfood. Some countries consider horse meat a delicacy. Maybe this still is going on. There are adoption programs but only richer people have ranches or farms to support them.
I used to see hundreds of rounded-up wild horses at the animal center by Reno, NV, and one time highly favored humane treatment. This hasn't been an issue in the media for awhile, but also wild burros were the target of shootings, by no less than the NPS (in Death Valley). In the 1970's the SC had barbeques where a burro was cooked in coals under the desert floor. A popular event, attended by many DPS'ers. They must have tasted good as this event was run for years. Myself, I never had any of this, but many SC'er are hunters by a matter of course.
We had MLC SC scoping for their hunting trips on peak climbs, to return and bag some deer if it was seen to be a good area for that.
BTW, one of them being opposed to eating meat, but favoring hunting prompted me to note, "Kill for food, watch out for A--- C-----, but kill for fun, bring plenty of guns."