I think I might be on to something that contributes to the problem. The built-in "KoboldGPT chat" option puts some example queries in its context memory. They aren't very long responses so I think it's just seeing that and using it as a guideline for what to say which results in shorter answers.
If I use the "new chat" option instead of "KoboldGPT chat", it makes it so that nothing is in the context. No prompt and no memory. This way when I tell it to write 500 words of crap, it doesn't quite write that much but it's a lot better than before. Pressing enter to make it generate more text works more often this way too.