Playing devils advocate here, it's because removing a function is not always as simple as deleting the lines. Sometimes there are references to that function that you forgot about that the LLM will notice and automatically update for you. Depending on your prompt it will also go find other references outside of the single file and remove those as well. Another possibility is that people are just becoming used to interacting with their codebase through the "chat" interface and directing the LLM to do things so that behavior carries over into all interactions, even perceived "simple" ones.