There is very little paperwork required to fire someone.
If the employee is still on contract (ala contract-to-perm) just collect their badge and be done with it.
If they are a W-2 employee with benefits, you hand them a few benefits notice forms and send them on their way.
If they apply for unemployment, the company will get a notice that the former employee has applied for benefits.
Plus there's the added risk of hiring "duds" that are also minorities. And letting too many of them go will make it look like formal discrimination. Which is a much, much more expensive mess.
And then there's this issue of finding the duds. Easy for the people on the ground to spot, but less so for management and HR, which will require some form of reasonably accurate performance evaluations.
Reality is otherwise. Lots of paperwork involved (for both hiring and firing). And leads to a not-too-great work culture.