I don't know if it is really that uncommon, in my experience. Any time that I am going for a course evaluation, or just to see a course that I've heard is interesting, I won't carry a scorecard. Also, a lot of times that I'm just going out to enjoy the course with my son, we don't keep a score.
There have been a couple of times where I was on the cusp of a personal milestone and didn't know until after the round. I used to be very superstitious about not adding up my scores until after finishing on 18. I'm not superstitious about it anymore, but I still don't try to keep a running tally as I play.