I said even at company friendly companies. Basically you'll see this happen even at companies where you CANT just switch job to get a raise (eg: companies that give out RSUs and had huge stock value bumps, making it unlikely you can get the same elsewhere).

I've seen it happen many times. People who got promotions after promotions and are paid absurd amounts, and after 2-3 years will jump ship anyway, often with a pay cut to join their friend's little startup.

Which is fine, its their choice and if they like that better, they certainly can go for it. That doesn't change that it's basically cultural at this point. Software engineers jump ship really quickly, even if everything's perfect (which, admittedly, is rare). I've done it many times myself.