It’s because they don’t see them as people, they see them as violent criminals that the world would be better off without.
If you step into their shoes for a minute, and one of the criminals you just successfully took off of the streets said they can’t breathe, your first thought might be “good. Maybe that’ll teach you a lesson about doing crimes in my neighborhood.” Your second might be “I wish I could shoot you right now and get this over with, but maybe I’ll get lucky and I can say I didn’t hear you.”
Conservatives in general think this way. That's why there was a desperate need to find something to blame Trayvon Martin for to justify Zimmerman's killing him. It's why they bring up the fact that Kyle Rittenhouse killed a registered sex offender as if Rittenhouse was somehow aware of that. It's why they bring up the fact that Eric Garner was selling loose cigarettes, as if that should have been a death sentence.