I've tried this approach of instructing the LLM to look for opportunities to abstract, but it's not good at finding the commonalities after the fact, when possibly related functions have already diverted unnecessarily. It writes "sloppy" code, that is to say code that is locally correct but which fails to build towards overall generalizations, but that sloppy code is a cul-de-sac: easy to write, but adding to messiness, and really tough to improve.

When a good programmer writes a new feature, they are looking for both existing and new abstractions that can be applied. They are considering their mental model of the whole system and examining whether it can be leveraged or needs to be updated. That's how they avoid compounding complications.

In order to take a big picture view like that, the LLM needs the right context. It would need to focus on what its system model is and decide when to update that system model. For now, just telling it what to write isn't enough to get good code. You have to tell it what to pay attention to.