Lawyers put the money up for a cut of profits. If legal claims could be sold then someone else could buy the claim itself and class action wouldn't be the only recourse for the poor.
Lawyers who work on pure contingency settle cases for pennies on the dollar because they can't afford the risk of going to trial. Especially in toxic tort cases, where the experts are expensive and the burden of proof is much higher than what science can easily satisfy (more likely than not, the injury would not have happened but for the defendant's conduct).
Legal claims can be and are sold to entities that aggregate them and bring the lawsuits themselves. That's probably better than the class action system but still leaves victims getting a fraction of their damages and perpetrators paying for only a fraction of the costs.
Another libertarian-ish solution to toxic torts, which I've never seen espoused, is to simply recognize that pollution is a form of violence and make it illegal. Then, people who want to pollute could transact with the potentially affected parties to pay them to shift onto them to bear the risk of harm from pollution.
