Simple - the backlash Bungie received back in the day for doing so.Odd, I always thought the Arbiter’s inclusion was fairly well-received. To be fair, my friends and I thought it was super cool but didn’t bother to look online or anything to see others’ opinions on it.
I don’t mind it as much now but back in the day, all I wanted to do was play as the Chief. I know i’m not alone in this and there were articles about it etc.
If you’re a fan of MGS, it felt like the Raiden situation all over again. There’s a reason why both Kojima and Bungie reverted to the original protaganist (well, Big Boss is Solid Snake for all intents and purposes).
The Arbiter was good for story building but given the choice, i’d still rather have Chief as the main protaganist and I am glad he was in Halo 3
I mean, it does provide an alternative look to the Covenant and does well to 'humanise' them but there was some initial backlash. It'd be foolish to say that
most people disliked it as frankly this cannot be proven but I think that Bungie making a point of Chief being the main protagonist in Halo 3 before its release may indicate that it was at least controversial.
To quote a few sources:
"Halo 2 gives up some of its focus from a storytelling standpoint, which becomes especially apparent once you finish the campaign. A great deal of attention is paid this time around not to the humans struggling for survival, but to the Covenant and what turns out to be a major political upheaval within their ranks. You spent the first game indiscriminately killing these fiends--yet now you're expected to be sympathetic to them and their hatred for humankind." (Gamespot, 2004 - https://www.gamespot.com/reviews/halo-2-review/1900-6112628/)
(Regarding Master Chief) - "The first game gave you just
enough to make his status as “Humanity’s Last Hope” something that truly felt epic and intriguing.
However, the structure and pacing of Halo 2
dramatically reduces his role in the game, to the point of nearly being misleading. Look at any of the trailers, any of the commercials, any of the marketing, and it’s clear the Chief was being touted as Mankind’s savior in its darkest hour — when in fact he’s reduced to a background character that’s barely there for half of the game (at least, that’s what it feels like). And it just seems odd to me to take a nearly iconic figure like the Master Chief, and do anything that might diminish him. (Opuszine.us, 2004 - https://opuszine.us/reviews/halo-2-2004-bungie-studios)
Granted, one is a major publication and the other is one admittedly i've not heard of before (you'd be surprised how difficult it is to find 2004 news articles!), it does somewhat demonstrate the confusion/disappointment in the Chief not being playable.
However, that said, the same sources also say:
"To the game's credit, all this adds some newfound complexity to the story (even the collector's edition version of the game's manual is written from the Covenant perspective), and the plot itself is executed quite well." (Gamespot, 2004)
Furthermore, the Arbiter's inclusion was also a 'cover-up', with alot of these reviews making no mention of the switch to the Arbiter. I think IGN demonstrates this in their review:
"Bungie has wisely placed heavy restrictions on what can be revealed regarding the story of Halo 2
. In fact, I can only talk about the first three chapters, which center on Master Chief's arrival to Earth and subsequent combat in the streets." (IGN, 2004 - http://uk.ign.com/articles/2004/11/08/halo-2-limited-collectors-edition)
To be honest though, whilst I initially disliked it, I do not mind the Arbiter's inclusion in hindsight. We now know more about The Covenant than we ever did in Halo CE, their political class and internal struggles, the impact of the first Halo game and more. I am glad we got to stay as the Chief in Halo 3 but that said, we did gain a great deuteragonist in Halo 3 and a good returning character in the 'Reclaimer Trilogy'.