Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Yes, of course they burn out and get less productive, I didn't say they wouldn't. You're proceeding from the assumption that your employer gives a hoot whether you're burned out or not. Being a "team player" for most workers means sacrificing your time and health for your employer's benefit. And if you're an "exempt" employee, your employer is not required to pay you for anything over 40 hours in a week, even if you work 90.