I think the answer is practice, for a few reasons. One is obvious: conversation is a skill. Just like a novice chess player can spend 5 seconds figuring out which squares the knight can move to while an intermediate player spots a fork to force trading a strong bishop or exposing an overworked queen, exposure to similar situations rewires your brain to work faster in those situations.

Another reason, though, is to me one of the main benefits of social interaction in the first place: The brain rewiring also makes you think about what other people would think, want to hear, say to you, etc, even when they're not around. That sure can give you better answers in conversations, but more importantly, I think this is just genuinely a nice way for the brain to be. In the same way that dogs are happy playing fetch, humans are happy living with other people in mind. Maybe because it feels like not everything is your responsibility, or that you worry less about what you should be doing, or that you look forward to laughing about disasters later... I'm not entirely sure. Whatever it is, it's nicer than the alternative.