Have you been to Twitter's SF site? It is a weird place, between super sketchy and plainly empty, what is missing is the peace of mind, definitely a valid reason to leave. It has all the downsides from being in the downtown, while none of the perks remain in today's SF.
Talent pool isn't a real issue for Twitter now, under Elon, I don't think they truly prioritize Twitter over any of his other companies, the mission is to keep Twitter's lights on, that is it, the website/app had basically stayed the same after he took over, what talents do they really need, I don't buy it.