User blog comment:N7EagleEye/New Mass Effect 4 Details/@comment-4973403-20121021014743/@comment-5607780-20121024221319

Well, I think that's because ODST was just a spin-off, it wasn't Halo 4. If it were and Master Chief was dead, I'm pretty sure Bungie would have put more effort into developing the character, and it is also notable that Shepard, as great as he may have been, was not the last of his kind (or at least I don't think he was), unlike MC who is the last Spartan. Since he is the last Spartan, he is virtually irreplacable.