This is how the market works. The reason you don't screw your employees like this is not just because you're a nice person, but because it costs you money in the long term.
Alas, market mechanisms aren't such great protectors here. They work best with large populations of similar events, where "average" behaviors can signal expectations and volatilities can be estimated on a fairly stable basis. Endgames offer the unethical opportunities to reap excess rewards without market penalties.
Hopefully, there will be enough information to know just how screwed these people are (or aren't, I've seen gossip that several were late-comers) and the VC / executive players involved. It's possible that these decisions make some sense, but it sure looks bad at first glance.
Funny how people thing this system could ever work.
Companies are the original trolls, making up new accounts and coming back without any negative karma or legal responsibilities. As long as corporations are separate from the people running them it's a joke.
Leave, if there's any justice in the world.
This is how the market works. The reason you don't screw your employees like this is not just because you're a nice person, but because it costs you money in the long term.