I've been saying for years that stock grants/options/RSUs are like playing the lotto, and salary/benefits are more important. They're also a tool to keep people in roles they no longer want, because of a promise of a great payoff someday.
To add to that, it's not like when you join a low-performing company you can just leave because you think you can get better value somewhere else. The cost of switching as an employee is very high.
Obviously it's a bit less of a gamble than the lotto, but it's not like decisions that were made 30 days ago are being played now, it's much longer term than that.
You might not be able to sell the shares you receive, but you should be able to exercise and hold them.
You might do this to manage tax exposure (to get the clock started on long term capital gains treatment and to make further gains capital rather than earned income).
There can be very serious tax consequences if the spread between your strike price and the FMV is large enough. The IRS doesn't care that you can't sell shares to pay the taxes. They're still due that year.
That said, you can probably do the math to stay outside AMT by limiting the number of shares you exercise. It's so hard to know whether or not to do that. I imagine a lot of employees felt pretty good about their WeWork options at the beginning of this year. I imagine. I don't know anyone there.