As I understand it (not completely), according to the SHIELD act, the losing party in a patent dispute has to pay legal fees for both sides, which are usually substantial. If the lawyers who really own the patent represent themselves, they are in danger of having to pay out if they lose. So they effectively hired a plaintiff that they could 'represent'. Handing out 10% of the proceeds if you win against halving the costs if you lose is a reasonable hedge.

However a legal firm is not supposed to do that, which is why they are in trouble.