Because it benefits employers to have desperate employees. If your short-term survival is tied to your job, you'll be willing to take a lot more abuse (and less pay) in order to maintain your core needs.

You literally cannot have comfortable life for the majority of society under a free-market system because it relies on the threat of being outcast from safety. The most socialist era of this country (1930-1980) is widely regarded as the American "Golden Era". I don't think that's a coincidence.