That's assuming that job openings are aplenty. The reality in most cases is that if the company doesn't like me, they can just wait for the next candidate. But if I don't like the company, it doesn't really matter because I need to pay the bills next month.
(inb4 "What happened to your fuck-you money?" As if it's always the employee saying "fuck you".)
If both parties sign an agreement with complete agency, who is getting abused? How can it be "unfair" if you both parties freely agreed to the exchange?