When you sign, there is a notarial act, and a video of you shaking hand and saying out loud that you understand this is a Ponzi scheme and you might end up loosing all your money, there is also some drug tests performed to make sure you are not under the influence of any drug, and some psychiatric evaluation to make sure you are not disabled in any way.
[.] Another thought slightly off topic: can I sue a Las Vegas casino because I put $100k on Red but the ball ended on Black and I lost everything? They even facilitate drugging me with C2H6O!
I don't know the actual answer (and it would be difficult to convince me that anybody has all the data either) but many people "experienced" with startups believe that so many more options come out worthless that cash is strictly better, better expected return at lower risk.
however, in the same way that the freakonomics guys explain people playing state lotteries even thought they are "not worth it": state lotteries (and startups) offer some of the few chances that most people have to actually get rich, so even though they don't pay off on average, they are "the only way" and "worth it" to some people. Not claiming that these people have clear ideas about either expected values or risks involved, but they have clear ideas that "it's the only way". For workers at many skill levels, they may have a sense that in their industry they won't be too much worse off in the long run so why not take a shot.