It's probably tied to fundraising. Execs probably have "key person" clauses and need to negotiate stock or secondaries as part of the deal.
Rumor is the minimum check they'll accept is $250 million. Valuation in the $150 billion range.
It would be surprising if these exits weren't in some way connected to the fundraising. (And not sure if these exits will be seen as a positive or a negative to would-be investors)
Or the execs figure a ~150x growth ride in 6 years is about the best that they can hope for and are ready to bounce. If I were in their shoes I'd look to take out 50-100 MM and decide what I want in life.