...holy shit, you're right. I just checked, and in the past decade, Crash and Gladiator were the only ones released before October prior to the awards. In fact, at least half of 'em were released in January, barely weeks ahead of the ceremony itself.
Why do you think that is? Distributors trying to release "Oscar bait" closer to the awards, or Academy voters just being too lazy and/or senile to remember any movies from more than a couple months ago?
But it seems to be a recent phenomenon. Go back another decade, and watch the pre-September award winners rise to almost half.
Well you didn't do a very good job at looking stuff up because Seabiscuit was released in July and it was nominated for Best Picture.