Why are some clubs not listed on this site even after someone tries to add them?

Just wondering. There has been a SC in my hometown that has been established for many years (changed names sure but they all do) and it has never appeared as a listing on this site that I know of. I have attempted to add it myself and it has not ever shown up. Makes me wonder why and also wonder if there are other spots in other places I could miss out on since I generally only search here when traveling. (Yes, I Google too so maybe I'd catch it but this is obviously the premier resource.)