I think there are a number of reasons. Or at least there were for me:
- Cost. It's expensive, and therefore it's something that needs to be budgeted for.
- Little perceived value / Arrogance. I spent time as infantry and thought I knew how to use a firearm effectively and safely. It took a trip to Gunsite to discover how little I really knew. You don't know what you're missing until you've gone to training. I think this explains why so few people have trained, but those that have seem to go to multiple courses.
- Time. Family obligations mean it's not easy to take a week off to attend a course across the country. When discussing vacations it's the rare wife that says "sure, and I'd like to go to Gunsite with you."