TBH, I'm not so sure it is a fitness level issue (well, not directly at least). I believe the game plan (the one and only one TB seems to have) is to play high up-tempo footy from the start and try to get a jump on the opposition... and something that we have actually executed reasonably well.
The problem as I see it is that this type of high intensity strategy cannot be maintained beyond 10-20 minute bursts. In addition, it's actually physically and psychologically draining, and excess energy is expended. I assume opposition teams know this going into our games, and their strategy is simply to ride out the intense period, maintaining their composure and staying solid as possible (all while minimising the potential points damage).
Basically, I feel it's a psychological composure issue. It's a bit like a fighter getting emotional and swinging like a madman... if the other boxer maintains his cool, he will simply negate/defend the wild swings and wait for the other fighter to gas before coming home over the top.
I don't know... it's just a thought.