They generally let people volunteer to be on call. But since everyone wants their weekends and evening it’s usually the same person. One of the other devs and I have been on primary rotation for about 2 1/2 years now. It’s a shame more employees don’t compensate for on call better. And honestly our teams on call is not a regular occurrence it’s maybe once every 2 weeks we’ll get a call for something that’s a 5 minute fix.
If Alex was previously on-call from time to time and got a raise to account for that typical amount of on-call, it sounds like you think that's fair? (It does sound fair to me.) Then, Bailey is hired at the same exact pay as Alex and also has to occasionally be on-call. Is Bailey truly "getting nothing"? Is Alex's pay fair and Bailey's identical pay unfair? I don't think so.
If you want to pass a law that requires employers to divide up pay differently than they currently do, that's totally fine; in some corner cases, it will result in a net pay increase for lower-paid employees.
It could be called an edge case, but when the on-call pay is built into the base salary, it creates the expectation that a person is never off the clock and no time is truly their own. It also removes the incentive to minimize on-call work.
It's happening all the time. Lobbied legislators will give some token QoL improvement for the masses and then give the 0.1% a nice big gimme in return.