It's because the typical leftist is a self-centered narcissist who lives in a fantasy world of their own making. When they think up the questions and the gotchas and their "witty" quips, they've already fantasized the entire conversation in their mind, already congratulating themselves on how smart they are.

Then when they have the actual conversation or interview and it doesn't go as planned, they assume the other person did something wrong. The other person is stupid. How could the other people not see things so clearly as them? How dare the other person challenge them?