One of the many idiosyncrasies of the English language.

The sentence

> Don't make fire rings where they already exist

means both:

1. If there is an existing fire ring, do not re-use it. Make a new fire ring somewhere else instead; and

2. If there is an existing fire ring, please re-use it. Do not make a new fire ring somewhere else instead.

What they _meant_ was the second interpretation, and not the first one.