You know what else killed a good amount of monkeys for their tests? Pretty much every single Class 3 medical device out there. Neuralink didn't do anything far outside the ordinary with their tests, they just got a lot of media attention because "Elon bad".
Medical device testing goes through animal trials before human ones. Those trials use monkeys. Those monkeys often die. The only unusual thing about Neuralink's tests is a lot of people pretending like they suddenly give a shit.