The advantages are too significant. If a company of sufficient size isn't doing this, they're doing something else. Statistically, employees cannot win; there may be outliers where an employee prevails, but in the aggregate, the company will win — and that makes these draconian policies worthwhile.
Companies enjoy economies of scale when it comes to negotiating employment, because they hire over and over and over again. Meanwhile, individual employee candidates must reinvent the wheel with each negotiation.
If you ever end up in court or arbitration, the unfathomable resources that the company can bring to bear means you're not fighting a fair fight. Our court system is by and large for the purchase of victories by those who can afford enough lawyering to exploit every advantage.
The only way to fix this is through government statute to change the labor market. The way the market has been constructed, employees will forever be on the losing end.