Here's the quote from the Facebook page why they don't publish. It makes complete sense to me:
There is no malice intended in not publishing our route. We do not publish the route of the Motorcycle Cannonball out of concerns for the safety of our riders. It is our number one priority. It's a wonderful experience for everyone when they meet people long the way, are assisted by enthusiasts, and get to talk about their bikes. We encourage people to come to our stops and meet the riders. Riders love the interaction when it's conducted in a safe environment.
Unfortunately, we have people show up to ride along, sometimes trying to join the group and this puts EVERYONE at risk. Modern day riders rarely realize the nuances involved in jockeying these old machines. It takes space, stopping is slower, and manuvering on a narrow, rough road is dangerous enough without having to avoid some body who zooms up to get a closer look. I have had several riders come to me on both runs and ask if something can be done about this since it scares the hell out of them. The fact that someone cannot understand this, tell me how little they know about riding a vintage bike. We simply ask that everyone please respect our riders.
Riding round the world on an old Ducati 250
Saving up for Round 3
Not Ted Simon since 1970 (tm)