And this is how we absolve people of all personal responsibility. Such companies would not pay people that well if they were so fungible.
There is no such possible binding rule either, a point that is so obvious that any smart person claiming otherwise is clearly up to something.
We make binding rules all the time. We didn't fix the ozone layer by encouraging people to quit their jobs producing CFCs. We lobbied for international regulation to ban them.
Influencing change is more complicated than that.
We live in a society that has systems of market competition between companies and economic/military competition between countries. There's not just one country working on frontier AI, and not just a few companies in each country either. The incentives of these systems ensure AI advancement will happen quickly from here on out, no matter what, absent governmental action.
An individual researcher leaving the company does nothing, other than give their seat to someone else who likely doesn't share their same concerns.
Alternatively, using the influence they do have in their position to directly try to advance AI safety research, advocate for govt action, and make public arguments attempting to persuade the public to pressure the govt to act when they otherwise wouldn't be inclined is far more likely to impact things for the better.