I'd argue that 99.9% of the time, they don't. How often do people want to sue their employer, anyway?
I've worked at two big-name companies, and I think they both had arbitration classes. I don't remember for sure. Never mattered.
In theory, you could use that clause as leverage for a better salary or benefits or other positive outcomes, but in practice I doubt that there are any cases of employment contracts where you give up this right for anything other than 'the right to sign the employment contract'.
I agree that these sorts of clauses should be banned, but "never sign a mandatory arbitration clause" is overly simplistic advice.
Unless one thinks small violations of workers' rights can make themself worse off than larger violations, they benefit from protecting their class rights for the collective effect.
The point is that it's overly simplistic advice to say never to sign such a thing, when there are potentially huge upsides (getting a high-paying job that treats nearly all employees well).
The police are protecting you because they offer a deterrent to crime, and the civil law protects by providing a deterrent to your employer fucking you over. Signing away your right to sue your employer when they give you the shaft is just as stupid as signing away your right to call the police when someone steals your car.