Because OpenAI cannot offer them competitive compensation, anymore. Not when they can court VCs and get hundreds of millions of seed funding to setup their own

Because OpenAI cannot offer them competitive compensation, anymore. Not when they can court VCs and get hundreds of millions of seed funding to setup their own AI startup. Also OpenAI is by this point a mature project so lots of people might feel a bit stifled in their freedom and they might be dying to explore new ideas.