Eh the whole point of being on call is that you are effectively assigned to ensure that you're ready to jump on incidents quickly at off hours if needed.
And that value is usually defined by the likelihood of incidents and the impact of these.
If you constantly have incidents that are critical, you can either spend the engineering hours to fix the problems once and for all. If that is not possible because it's a different problem every time, it might be important to invest in more engineering resources and have them work shifts.
Printing for example has such a system where the impact of a stopped printing press can be catastrophic because no newspapers tomorrow. Thus there are on-site engineers that are paid to sit around and wait for a press to stop working.
If the occurrence of an incident is rare or the impact of them is basically nil for whatever reason, feel free to consider on-call not that important. Maybe an SLA of 6 hours is acceptable in such a situation.
If incidents are happening often and are important yet you do not want to spring for extra engineers but have your existing staff work on these on top of their regular duties, you need to come up with the right incentives. Massive pay helps to sweeten the deal and also provides incentives to prevent pages.