Well, the Trump Tower meeting happened. That, in itself, means they colluded. Attempted collusion is their only defense right now. So they need their guy to do whatever he can to justify saying as little as possible.
So, imagine I met with a hitman to talk about killing my wife. A month later, my wife is dead. OH, and it happened hours after I went on TV and said "Hitman, if you're listening, please kill my wife." If I were to say "yes, I met the hitman to discuss killing my wife, but we couldn't reach a deal," what good is that as a defense? It's ridiculous.