A bunch of possible reasons:
- A lot of people don't know what they are actually worth and undervalue themselves
- or they do not understand the caveats of things like dilution and classes of stock
- or they were offered stock in units of shares without knowing the valuation
- or they accept a job and relocate to the Bay Area from a reasonably-affordable place and mistakenly think that a $100k/year salary is hitting the jackpot
- or they were persuaded by the founders that the company was going to be a rocketship without fulling knowing how to judge potential in companies or in the personal traits of the founders themselves (we're not all superstar VCs) and then it didn't turn out to be the case but they didn't want to eat the sunk cost with their unvested shares (takeoff was always just ostensibly around the corner!)
- or they didn't realize just how much more FAANG actually pays than late-stage startups or even other top-tier companies (even Glassdoor is wrong)
- or they preferred to take on more risk without fully understanding the reward aspect (the survivorship bias here in the Bay is real, as enforced by a tough housing market)
- or they previously worked for a big company with poor culture and were turned off by it and decided to only work for startups
- or they weren't prepped in the art of negotiation
- or the founders acted against their employees' best interests and took an early buy-out offer that brought everyone in as acquihires of BigCorp for cheap
- or the founders took money off the table for themselves with zero intentions of ever doing anything favorable to the employees that would actually let them to liquidify such as trying to go public or sell the company, while still keeping up the whole carrot-on-stick shtick