The rancher probably wanted to shoot the bull himself for the meat.
Or put down humanely instead of used for target practice. The rancher could have put him down with one bullet.
It is possible he wanted to keep the animal from being shot, too. Means of production and all that. The biggest reason the animal was shot may have been that it was agitated, not that it was irreparably damaged. (Not enough info to say).
A good cowhand can get a critter to behave, back down or move along when someone not so well versed in dealing with livestock will make a mess of things.
Believe it or not, YEARS ago in Oklahoma my uncle, a well known drinker(?)was going home with his wife (a well known idiot) in the car. He hit a bull,which limped off with a broken foreleg, and smashed his car up real bad. The Cops pulled up, asked her if she had been driving she said “No my husband was.” They asked ‘ Where is your husband ?’ She said “Oh, he’s off shooting the bull.” They were getting ready to handcuff her when Dutch showed up from the side of the road.