As a competitor or audience?
As a competitor it’s the same as wanting to compete in any sport. Why do adult ammies run marathons or play tennis? You have some skills to use, you like the sports ritual of everyone doing the same limited formulaic thing to see who is best at it, you like the comments of a judge, you find the total milleu interesting and exciting, it gives you a goal, it gets you somewhere new, and there’s a social aspect.
I have to say that my personal professional background is in the arts where you are rewarded for originality. If you can do something well in a way no one else can, that’s the height of acclaim. Hence my horse can help me decorate a Christmas tree at our holiday open house. That’s the total opposite of the sports mindset where the activity is narrowed down drastically and everyone is evaluated on the exact same criteria.
However if I had access to a horse that was likely to do OK at any given discipline I would likely do a few local shows just because.
My job category is in fact very competitive at least at the start but as I said, you compete on originality. I know how long it took me to professionalize my ammie skills and how much that changed how I felt about my skills. I feel like I don’t necessarily have the mental energy at this point to professionalize my riding and that it needs to stay as a respite from all that. But I could easily see how showing might become a central goal. Why not?
As a teen I went to every local playday schooling show I could hack to because it was a community event. I got a lot of 4th place ribbons in large but mediocre classes of 1970s backyard horses. I can’t see treating shows like that as an adult, they are too expensive and formal.