Conversation so far:
When did Robbie O'Connell join The Clancy Brothers?
1977
Why did The Clancy Brothers decide to add Robbie O'Connell?
Their recently deceased sister Cait's son, Robbie O'Connell, was an up-and-coming musician in the US and in Ireland; They asked him to take on the role Liam had vacated.

Question: Why did Liam leave?
Self-contained rewrite: Why did Liam leave The Clancy Brothers?