Tom’s post below made me think that mayeb an issue here the vanity of the writer; after a time, being a top-class gag crafter just isn’t enough. They wish to be seen as dramatists, commentating on the human-condition through the eyes of noble members of the working class who populate their scripts. The more they push forward this, the more they forget gags and push character emotional plotlines, not situations (it being a sit-com, after all) where the character of the character is a crucial part of the set-up of the gag.
Take Frasier (no, missus, please!) where they don’t indulge the melancholy of the Cranes. They want us to feel sympathetic to the Cranes, so they let us know it’s there. It ultimately a classic farce with the humour on the gentle and affectionate spectrum, not abrasive and scabrous. But they are pompous and that’s where the gags come from; most arise from the failure of the Cranes to do something really, really simple, such as say ‘excuse me’ to someone and the humour moves forwward until it arrives at the end point of a farcial new timeline than started off at a tangent from reality when Crane pomposity made sure something really simple didn’t happen. The melancholy is a crucial comedic device, not a conceit for the writers.
All of which make me think here that there’s something here about collegial writing as common with US shows and the single-writer model favoured here. A writer on their own is more likely to feel the need to get ‘arty’ and less likely to have someone remind them that ultimately, it’s about the gags, stupid.