That is exactly the same on any review site though.
Even on trip-advisor.
If a place is great when it first opens, it gets 5/5 reviews. Then it goes really bad and starts getting 1/5 reviews, anyone who looks at the site will see it getting 3 or 5 out of 5 on average.
People will look at the most recent reviews and note any changes/read what people are saying, that is just common sense.
I guess I left out perhaps the most important point: the number of people traveling an AC route is pretty small compared to the review sites you may be used to in larger towns and cities. I'll make up a number here: 1% of people who go to a restaurant, motel, or campground will review it. In a big city, the new bar may get 5 reviews a night. On the TransAm, there may be 5 reviews per year for a given 30-50 mile stretch (about one day's ride). On some of the other routes, it's probably less than that.
Sure, I can see the potential benefit to a future bike tourist if you had a fully populated, active review system tracking your route. Perhaps if you were to set someting like that up, AC would link to it. If it were populated, active, and accurate, they might be persuaded to take it over. But as I wrote previously, I don't think it would be a wise use of AC's resources to start something like this.