Depending on the work culture, out of hours event is a minefield. At the very least, you should have an opt-out possibility and not looked down upon if you do opted-out.
Totally voluntary. Work just pays for them. A number of people opt out and no one judges them.
How do you know what your coworkers think?
That sounds ... very strange. Weekends aren't generally speaking "office hours", and more importantly also not "working hours". Having an "out of office event" in my world is when you're doing work, i.e. it's during normal working hours, but you're not at work.
Having frequent work-related "events" on weekends sounds like a total bummer.