Well, I assume it's that drastic to both discourage rogue nations and because most alliances are rich. I doubt a rogue nation will come from our alliance, and if it does by then we'll be making enough money to the point it doesn't matter anyways.
Most alliances aren't that rich. You have to remember that you can only hold 150% of your GDP, which means the richest nation in the game can only have on hand about 11000k. Let's average out the current GDP of our members, 302, and double it (assume this happens maybe in a few weeks or a month), so we have about 600 GDP average between members, so in 12 hours if ALL of us get online and pay all of our money, we can pay the 33000k and have 3000k left over. Assuming we are all online and able to pay, and it's a 500 GDP nation that get's attacked. God forbid one of the 1000+GDP nations gets gassed 2 or 3 times, because then it is going to take a day or two of everyone paying. The issue is that not everyone will be online at one time, so it may take 3 or 4 days for reparations to be payed out, or they may never be payed out. Also the whole "The timeframe for all reparations shall be decided by the chairman on a case by case basis." is a horrible, horrible system. Oh, you had one of you members take out 400 GDP from someone? You have to pay $80000k in 5 turns. It really needs to be a mathmatical formula if the 200k rule still stands... I think something like below would make sense.
T=P/(S/2)
Where:
T = Turns to pay debt
P = Total payout
S= Sum of alliances GDP