Congratulations, you've made you entire team on call year round.
I don't read work chats outside of core working hours if I'm not currently on-call. In general, most people shouldn't. Doing so is awful for your stress levels and work-life balance. I did it for more than a decade, burning out twice in the meantime, and things have been much better since I stopped.
The goal is not to need on call, because you BOTH have a stable system that requires rare off hours interventions, AND you have a team that owns that and is bothered rarely enough to not need to have a formal rotation.
On call systems with stable systems in my experience tend to be a real problem because people lose the on call urgency anyway.
TL;DR - the problem is your system, not being on call or not.
An average company with engineers who don't hate their job, staffed adequately, it should be a stars align kind of scenario where you can't get someone on a weekend. It's a simple matter of probability, and if that probability looks grim, either A. you're understaffed, or B, your staff is underengaged.
I have fixed customer outages on my phone out having a good time more than once. Usually with another engineer happy to help. Not just at one company. If you need an on call rotation, your culture sucks. I'm not advocating that people live to work, I'm advocating that people work at places where people enjoy working with their peers and their product enough that an occasional blip isn't a big deal. With the right infrastructure and the right people you should have this.