Would rather not have something half-finished that I have to pay full price for. I don't want huge gaping holes and obvious tell-tale signs of left-out content. Either get it all done in time for the deadline, or finish it post deadline as a "sorry, the evil powers that be made us publish this game before we were ready, but we'll finish it soon so you won't have wasted your $60 to $80." Or just scrub all signs of left-out content from the game so that no one is the wiser.
Which negative result outweighs the other? To have a game where lots of content had to be cut to avoid delays, or to have a game delayed at significant monetary costs to the company? Sure, you might get your nice game, but at the cost of the development studio going into a downward spiral that might result in them not being able to put out high-quality content?
And they already did delay Oblivion once. A second time would've been overkill. Just think of all the things that might've been cut had they not delayed the first time.