This might be a tongue-in-cheek rhetorical question on your part, but I can only imagine the Smith Rock folks are a little edgy and conservative around fire since their own employee started that huge fire down there in the 90's that torched large swaths of the state park, eh?
Which is not to say that it couldn't be managed appropriately now, but just pointing out the historical context to your question.
Even before the park fire you couldn't have campfires at the bivi site. I recall that as being a big reason why people drove out to camp at the grasslands in the first place.