Largely speculative (along with
some Ske7ch comments) but :
All advertising & coverage (I think the Gamespot interview didn't even mention the Arbiter) focused on the Chief & fighting the Covenant on Earth.
So when the "twist" happened, that
a) we would play half the game as an Elite &
b) we would spend well over half the game not on Earth
-> players reacted poorly. People weren't prepared to invest in him.
I think if people's expectations were better controlled, then there wouldn't have been such a backlash.
It was added by the frustration of the cliffhanger.
What annoys me is that Bungie didn't help improve player investment in the character with Halo 3. God Halo 3's narrative is so minimalistic and the bits that were left in...
*gets pointlessly worked up*