A better question is, why do US federal laws allow that kind of number mangling and contract swindling?

Since any contract can be full of tricks, it just means you need an army of lawyers even for the simplest things. It then gets really hard to actually do anything. And if you're poor, you're bound to get exploited by some obscure loophole.

Nobody takes net points. Plenty of people take points on the gross, which is fine. Studios know that talent has wised up to net points, but that doesn't stop creative accounting from screwing you over in other ways.

For example, one of Peter Jackson's main grievances when he sued New Line was that he had been promised a cut of the revenue from merchandising right sales. New Line sold the merchandising rights to its own sibling and subsidiary companies using a closed bidding process at well below market rates.