Right now the formatter is not used in CSV/Excel exports. This is a feature thanks to which if you ever wanted to import the exported values back into Jira, it would still work.
That said, we are considering different options of addressing this, as we realize in some use cases exporting with the formatter would be preferable. Unfortunately, I can’t share any details or dates at this point.
Hope this helps, let me know if you have any more questions.