A lot of people join a club because it's easier to get ice time. Some join because it's simpler for them to test as a club member than as an individual member. Some join because they have friends in the club.
Some join just because they love to skate and it's nice to be able to skate on a session that's not crowded with hockey players and people that can't skate at all. Our limit for skaters on a club session is 26 and that can be a big help to a skater that wants to work hard. And it's easier to get your music played for a program during club ice.
And some skaters join a club because if they don't join, then they can't skate on a team they want to skate with.
Don't be intimidated by the "everyone that skates in a club must be great" idea. Because that's not true. Yes, some clubs have high level freestyles, but they will tell you what those sessions are and you can pick another session to skate on.
I could probably go on about why to join a club, but think the above are some really good reasons. I have met some very good friends during my years with a club (both young people and adults) and these people are some of the nicest people I've ever met.