This has always bugged me since the first time I played Halo 2 way back when, just not enough to remember to post until now! Why do the Elites and Grunts simply turn around and stand there after Regret is killed? It’s weird the Elites, a race that runs on honor and a hatred for humans, would simply stand still and let a human get them from behind. I don’t care much about the Grunts since they’re mindless followers but their behavior is still interesting.
From a lore perspective, it may be complete shock that their hierarch has been killed. From a gameplay perspective, it would be really unfair and frustrating on the player if they were killed right after they killed Regret.
The game designers set it like that in purpose I forgot why