The idea is instead of having you enter the game before the Oblivion gates start opening, they should have had you enter the game after the Oblivion gates have been around for a bit.
The reason they should have done this is because that way they could have had most of the Rainforests burnt down by the Horror of the Oblivion gates, and only the epic hero would be able to stop the Hellfire from consuming Cyrodil, they'd still have to make a few Rainforests but it wouldn't be anything they couldn't have handled and they'd have a Lore friendly exuse for not making Rainforests in the game.
If they had done this they would also have had the advantage of making the player feel like he's in a real Crisis as there are more Oblivion gates and there's a feeling that the world will really end if you dont defeat this.
But instead they broke cannon.