There are so many laws and regulations on the books that we take the attitude 'if it's not illegal then it's OK'. There is no good reason that all recreational vessels shouldn't have a capacity rating, but except that the manufacturers know it will hurt sales. You're correct that there will be lawsuits, but the attorney's will have their hands full proving any sort of case. Any suits will be nuisance suits looking for a settlement. It'll remain legal to put as many people on a boat as you have PFDs for, and any captain who walks away will simply see a less experienced captain take his job.