I don’t think the Clubs ever intended to become cliquey, but it happens by default sometimes, because the main participants get older and greyer, and through longer involvement they naturally become more proficient as performers. Welcoming as they might be to younger performers, newcomers and those just startIng out tend to then feel intimidated by the more experienced and adept performers already there.
If I was twenty again and walked into a club or indeed a session, where everyone seemed to be quite accomplished and clearly older than my grandparents are, I’d probably think twice before going there again. It’s easy to see why open mic sessions are popular with younger performers, but it would be sad if we lost the Clubs and only saw the rather impersonal and unsupportive open mics survive.