Banks want secrecy

Banks have a vested interest in keeping the swaps market opaque, because as dealers, the banks have a high volume of transactions, giving them an edge over other buyers and sellers. Since customers don't necessarily know where the market is, you can charge them much wider profit margins.
Banks try to balance the protection they've sold with credit-default swaps they purchase from others, either on the same companies or indexes. They can also create synthetic CDOs, which are packages of credit-default swaps the banks sell to investors to get themselves protection.
The idea for the banks is to make a profit on each trade and avoid taking on the swap's risk. As one CDO dealer puts it, “Dealers are just like bookies. Bookies don't want to bet on games. Bookies just want to balance their books. That's why they're called bookies.”
Now as the economy contracts and bankruptcies spread across the United States and beyond, there's a high probability that many who bought swap protection will wind up in court trying to get their payouts. If things are collapsing left and right, people will use any trick they can.
Last year, the Chicago Mercantile Exchange set up a federally regulated, exchange-based market to trade CDSs. So far, it hasn't worked. It's been boycotted by banks, which prefer to continue their trading privately.