@mellotronrules there are no labor laws about what is an acceptable work week, only laws that say over 40 hours per week is overtime, so if someone is willing to work more they will be paid more for that time than someone else who's only willing to put in 40 hours, and salaried workers are often paid more with the expectation that they may have to work some overtime.
According to the Bureau of Labor Statistics, there were 7.1 million unfilled jobs so your point about employer leverage is largely invalid. Those jobs are unfilled because either there are not enough qualified people for the position, or the job doesn't pay enough, with either case forcing employers to pay more - not a great power dynamic for employers.
Employers have huge amounts of power as people don't just get to choose which "7.1 million jobs" they want. There are tons of constraints that prevent people from picking whatever job they please. Many of which have already been mentioned in this thread.
Also, you are making the assumption that people always have the choice to work overtime. This is rarely the case. People are often forced, either explicitly or implicitly, to work overtime and if they are salaried the compensation, if any, is minimal.