4. They Write Without Running Gags Or Catchphrases
Because it's so easy to fall back on the same line to make someone laugh. It's the same with a laughter track that cues you when to join in. Andy Millman commented in 'Extras' that catchphrases were a cheap laugh, and to take nothing away from the shows that use them, 'The Office' etc are ambitious not to recycle the same lines of dialogue. Brent is a character that is so well-rounded, so brilliantly consistent, that if you want to impersonate him, you might do "a Brent moment", rather like you would with Alan Partridge, Mark Corrigan or Norman Stanley Fletcher. These characters can't rely on a fall-back joke, and that's not only more exciting, it makes for more realistic television. It's not that "I don't believe it", "How you doing?" and "I'm free!" aren't funny. It's that catchphrases can sometimes sum up a character in a single line of dialogue, and Brent, Andy, Tim, Derek, Darren, Gareth, Dawn and Barry are such brilliant characters, they don't need to be boxed like that. Comedy is all around us, and Gervais and Merchant capture that perfectly.