1.) Developers don't understand what they are worth
2.) The culture of 50+ h/week working is pervasive
I think the point where we disagree is about the optimal behavior from the companies POV. Based on the exclusivity of existing condition eligible health care and collaboration by major tech firms to illegally collude to prevent competition for work, I don't conclude that it is a system which will fix itself. However, the only viable solutions I can imagine would be unpalatable to too many programmers to be enacted.
Having said all that (and established some of my statist liberal bona fides), I do not think abuses of at-will employment or overtime exemption demand legislative fixes; in particular, I think that it's far more likely that it would harm startups (and the employment market in general, for employees and employers) to regulate overtime for salaried employees or, worse, termination requirements for employees.