Engineers interested in cars or rockets have way fewer exciting options than web devs working at Twitter.
Anecdote time: I have an acquaintance who’s an engineer who works on nuclear power plant technology. They’ve wanted out of their current employer for over a decade now.
Why have they stuck around? Because their current employer is the only one in a several thousand kilometer radius with any use for their expertise, one of only a couple they could work for without leaving the country, and one of only a handful whose primary language of business is one that they speak.
Tesla, SpaceX, and perhaps even the Boring Company have much more in common with that situation than they do with Twitter.
I think smaller companies and upstarts have a chance to get some great talent that will be strongly considering their living situation and looking for something more stable, but I'm not so sure that Twitter is going to have its pick of the litter for a long time until it demonstrates a stable and mature environment to work in.
I have no doubts some persons will be very nervous and take the opportunity, and I wish them luck. I'm not so sure others will be as eager.
But replacing all of the random but critical bits of knowledge in the heads of the people walking out the door is much harder.