Why do you think businesses tend to be benefit the most? There are historically twice as many quits as separations, so workers are twice as likely to use "at will employment" to leave then having the Business use it to fire them. I can't think of any data to support the notion that the bulk of the benefits are not borne by workers, but if you have some, I'd be interested in hearing it.
I was thinking that for a company to lose an employee is not something negligible but usually not the end of the world, while, for the average person, losing their job could be a big deal. Given this asymmetry in power, I can imagine that the employee is the one that usually has to compromise on things.
You do understand that people with contracts are also laid off, right? The question is whether you get any better terms or are restricted in how you do something (for example, waiting for a period of time to end or providing additional compensation)