Why?! It's so sexy and matches the art direction of the game. It would have been perfect! It's so sexy it makes all the Covenant weapons all wet and horny. I can say nothing more lest I cause you to orgasm.
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343 stated that H4 was unfinished and that there was a lot they wanted to do but didn't have time because Microsoft wanted it out by a certain release date and scrapped a lot of ideas ( or hopefully saved it for H5)