Another reason to do something besides competing is just to challenge or improve yourself. I started riding motorcycle trials competitions last year, because after 20+ years of riding a trials bike, I wanted to challenge myself and improve my riding, and I'm happy to say it's done both, and been a ton of fun as well.
However with RC crawling, comps doesn't appeal to me that much, I'm happy with how I drive and I challenge myself enough as it is. Today when I went to my local crawling spot there was a small comp going on, all comp style rigs, just didn't look fun to me.