its unknown why they speak like that in reach its probaly because didnt need to insult the humans or talk to them in englishhard question. probs just a fault that bungi didnt notice.To prevent 3/4 of Halo 2's dialogue from being "Wort, wort, wort."In halo reach, Bungie wanted to give the game a more "gritty" and serious feel, so they figured that removing English dehumanized them further and made the game more serious. There is no canonical explanation for it i believe : )
Yes, it's not realistic to hear Elite sreaming : "Go, go, go, our leader is under attack!" It's better to hear : "Wort, wort, wort, Kaidon blargh mfff "