We're all a function of our experience of what is likely to break down and which will shape our attitude to risk. It's very similar to folks' views on home insurance and the level of cover people take out.
In my case, I do actually have spares of pretty much most key gear i.e. (too many!) basses, recently acquired spare gigging amp, couple of cabs etc. But I play pretty much daily at home and much less frequently out on the road by comparison, although I'm probably doing a middling number of gigs by BC standards. So for me if a piece of kit is likely to fail then it's most likely to happen at home, so I'm comfortable that if it all checks out and not showing any signs of being temperamental pre-gig then that works for me and my bands.
There are plenty of pro bass players I know on BC who have not had any issue over decades of gigging with their basses (refer to the OP's previous thread for examples) and are comfortable with not bothering with a spare bass for a local pub gig but might take one to a more distant wedding. And others who will take spares of all gear to all gigs. I personally don't consider either to be more "pro" or more "evolved" as bass-players as one earlier post suggested. They're just basing their decisions on their own experience and attitudes to risk, just as some folk don't want to start gigging until the autumn due to Covid-19, whereas others can't wait to get back out as soon as we are allowed to.