The monuments to individual regiments, brigades, etc. at most National Parks were erected by veterans' organizations like the Grand Army of the Republic, much in the same manner that a wide majority of Confederate monuments came about as the result of efforts by the United Daughters of the Confederacy. The Yankee Guv'mint, then as now, really sort of preferes that one not clutter up the real estate with all this stone stuff ;-)

Uncle Sam does provide a suitable monument for all of his nephews -- even the estranged ones who wore gray -- in the form of a marble marker for their final resting place. And in the end, that's the one that really counts.

Tom