I like the people in my club. They are nice folks and riding/volunteering at events lets me meet them and get to know them better.
I like the challenge of riding a brevet...it's hard, but not out of reach of my average cycling skills.
Having said all that I don't live and breathe for randonneuring. I have lots of other cycling interests that I am stoked about. I just ride brevets when I'm in the mood and they fit my schedule.