Because we should stand up for our ourselves. Other clubs (Sheffield Wednesday and Portsmouth) wouldn't stand for it. They shouldn't be able to arbitrarily and consistently contravene league rules without reproach because weak clubs like ours just take it on the chin every time.
But but the money - it isn't that much really. Difference between 4k and 1.5K (why do City fans talk of 6K allocations at the Ricoh, nobody has ever had that, certainly not now with the maximum cap set at 4K), when you take into account concessions, take off VAT and then factor in the much reduced policing bill, it isn't much of a sacrifice at all to preserve some self-respect.