1. Company needs to raise money
2. Company issues new shares
3. Board realizes "oh shit, this is a lot of dilution"
4. Board decides "okay, who is important enough to keep around" and issues stock grants to those special people to undo their dilution.
Founders and VCs have seats at the board table, and so are always important enough to get grants. Employees do not, especially after exit.
So the two choices left are
a) employees have no protection against dilution, therefore no protection, therefore shares are worth zero, or
b) employees are given protection against dilution.
You can say "b" is never going to happen. That's okay. It means that "a" and it's obvious conclusion happen.