Don't forget acquisitions though, you don't need to be public to be acquired and those deals also cash out vested employees.

We can talk about if that's favorable or not relative to an IPO, but public offering isn't the only way out. Actually, I expect acquisition is probably a more common exit for employees than IPOs.

Some larger private companies buy back shares as well to help employees with liquidity. It still sucks being relatively cash poor as an employee for multiple years when your company is valued at billions of dollars.