We're talking about a decade-old company with billions in revenue. If your job at AirBnb was your first chance to build any wealth, you never had the option to diversify. I don't think it's fair in that case to blame the employee.
I don't necessarily blame the management either. I do hope this reminds employees of private companies that their equity is only on paper until they are able to sell, and they should pressure management to give them the option.