Over 15 years it all gets lost. When they made the change, I was on a team that didn’t do on-call, because we were 24x7, so our pay remained the same. Eventually I got a new role, also without on-call. One day the boss thought it would be a good idea if we start doing on-call support. There was no pay adjustment for this, no new job I applied for where on-call was part of the deal I signed up for. It just happened.

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.