It's pretty common in the financial world. The US government doesn't offer zero-coupon bonds, so the big banks create special purpose vehicles that buy US government bonds, split the cash flows into the strips and the zero-coupon bonds, and sell them separately. If some pork belly futures trader wipes out the bank, at least in theory, the special purpose vehicle outlives the rest of the bank and keeps paying out those cash flows, and the pork belly creditors don't get those zero-coupon bonds you bought.

At least, I think that's the way it's supposed to work. I used to work at Goldman, and at some point, someone told me that the number of legal entities was roughly the number of employees. I'm not sure how true that was, but I'd believe it.

There are some good reasons to allow these separate legal entities, to allow orderly partial collapses of businesses to reduce the risk of cascading systemic failures. There's also something to be said about either keeping businesses small enough that failure of a handful of them won't collapse markets, or else single-purpose enough that they have less direct effects on multiple markets. The flip side is that diversification across markets should tend to stabilize firms, and larger firms are also more able to effectively diversify.