Like AstralPath said, the take a fairly large portion of the final payout, but more than that, when they are working on commission, they pay for all the costs, which isn't very tempting. For most laywers, if not all, working on commision, the have to be fairly certain of two things:

1. They have a good chance of winning the case
2. Their portion payout will cover (and preferably more than cover) the costs they put into it

Unfortunately, not both are true that often. So, many people are just left screwed over with no way to recover anything

True, but your settlement to recoup costs gets eaten by the lawyer, likely to leave you with very little at the end of the day. So the defendant gets a slap on the wrist, you get a pittance and you're still fucked.

I'd sue no matter what just out of principle, but just sayin' lol