Thanks, everyone, for the discussion. I believe it is, for sure, lawsuit avoidance. The Park also wants to close a huge section of Highway 101 to cyclists...the portion that goes around Lake Crescent. And, their policies about road closure to the ski area have drastically changed over the years.
I understand that unpaved roads are a different ball game for cyclists than for cars. But I have had a Park employee admit to me, off the record, that the Park has pretty much taken an attitude of wanting to limit access rather than promote it, in general. Also, the entire 20 mile stretch of road will not be without pavement for a full two years. I really believe if they are accomodating motorcycles, they can accomodate bicycles. Some people hike right up the road. Those people are not being banned.
I appreciate everyone's comments, and I will take all this discussion to heart.
Please, if you are inclined, consider writing not only to Senators Patty Murray and Maria Cantwell (both D-Washington), but also to the Park director, listed in my original post. Her email is listed. Thank you.
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury