It could be that Amtrak as a government agency is looking for ways to market itself and is using a historical exhibit to do that. It seems better to get folks to the train station, with a focus on those whom would otherwise not be inclined to use Amtrak's product. Most of those in DC who do not travel by train would now have a reason to see the exhibit and perhaps spend money on their next travel experience using the train.

I for one enjoy WUS and any exhibits would just add to the experience making travel a bit more interesting for the public.