You also need to consider that the median tenure at these type of companies are 2-3yrs[0][1][2] (1.1 at google!). In my experience that's not enough to get the full stock grants.

So even from those that could make it very few stay long enough to make these great riches your imagining.

[0] https://www.payscale.com/data-packages/employee-loyalty/full... [1] https://www.businessinsider.com/average-employee-tenure-rete... [2] https://brobible.com/culture/article/how-long-employees-stay...