They still have to be okay with the significant probability that they end up having worked below market value. Many of the smart people I know working at startups are perfectly okay with this because they love what they're doing and the potential big dividends is just a really nice bonus.
It would be really hard for me, in the current stage of my career, to justify working for a startup unless I knew the expectation value of the returns aren't at least comparable to traditional jobs. The investment money wouldn't be there either.
I wouldn't really be a smart rational economic actor if I hadn't judged it to be profitable over my other options, though I admit there is more to it than just money.
