Except there are plenty of places that expect 50+ hours/week and pay 20% less than market at least. Likewise, I'm sure there are jobs that pay market or better and get close to 40 hour weeks.

The market doesn't work as efficiently as you imagine it does, nor could it since companies do all they can to hide what salaries actually are (i.e. imagine trying to buy fruit when nothing had prices, no one would tell you what they paid, and you had to negotiate in private for what they cost you).