I think the simple answer is that Epic is understaffed for the task at hand. By developing the engine and game at the same time, it takes time away from focusing solely on the polish.
The UI is beyond a joke, compared to all it's competitors. The storyline would have been scrapped if any external audience\betatesters had been shown the cutscenes.
its more than just the engine and game, your forgetting about the biggest thing that takes away man power from "unreal"...that thing is "the gears name" epic is / has developed 2! gears of war games in 2.5-3 years...i guarantee that is taking at least 50% of the man power at epic to create and release those games, probably more! so right off the bat, "unreal" and the engine is down to 40% or less to then create an engine, keep it top notch, AND make another addition of "unreal", o yeah, and make it work on 3 separate platforms at once as well...
just reverse them for a min and ask your self, if Unreal was gearsofwar, and unreal had been the main focal point, as well as it has had 2 games released in 2.5 to 3 years, with most of the man power at epic working on it. how good do you think unreal would be, and how ****ty do you think gears of war would have turned out? its pretty obvious to realize the roles would be completely switched and reversed.
its the same exact reason why our 1st "bonus" pack wasn't anything bigger than a toy you would find in a cracker jack box. all the maps we got were just maps intended to be released at release, they were so understaffed maps didn't get finished in time, so they had to release the few maps a few months later. which is also why i believe we wont be seeing another bonus pack, at least not for a LONG LONG time, because any additional things they release will have to be created from scratch again, and not just left overs from a half assed release.
then on top of all that, they force them selfs to release the game before x-mas for PS3, cause we all know how many mommies and daddys buy their kiddies loads of games for xmas, so epic wanted to make sure to jump on that cash cow...but in doing so they shot them sefls in the foot by insanely rushing the game and basically completely cutting out the "polish" area of game development, as well as release the game with LOADS and i mean LOADS of other FPS's and games which in the long run i believe has hurt its numbers...they should have waited 6 months, and released it in the spring just like they did with 2k4, would have had 6 more months to polish the game, as well as they would have been releasing the game with NO competition, meaning much more units being sold, and a much higher online numbers.
either way, their was numerous reasons for ut3 being like it was, which most of them stems back to understaffed / rushed
as far as the UI, dont get me started lol, i just hope they buy the "uwindows" mod being created, and release it with a ut3ECE or a ut4, and have it as an option at install to use either "uwindows" or the "standard" GUI