Many who served in the military have trained at on-base MOUT training sites or other small scale urban warfare centers. Few of them are very large. Just a few streets & city blocks spread across a few acres. Maybe village sized. I've trained in an actual small city sized facility located in Israel. Still only a few square miles. All of them great for training up individual teams, squads, platoons, companies, or battalions in the art of street and building fighting. But...
Those facilities (even the biggest ones... like NTC's armored maneuver area) are simply too tiny for some types of training. Lacking frontage, square mileage, or lane throughput for maneuvering really large ground units.
Showing my age, but there was a time when NATO units used huuuge tracts of the heavily populated civilian German landscape for major maneuvers. Corps & Divisional sized formations rolling over highways, towns, cities, rivers, farms, villages, bridges, and fields. Hundreds of thousands of exercising troops scattered over the entire country simultaneously. Fighter jets and attack helicopters flying over every conceivable populated area. Battalions of paratroops dropping from night time skies onto village farm fields. Autobahns clogged with hundreds of tanks and thousands of vehicles. All of those units pretty much driving or flying wherever needed/ordered.
REFORGER was one of the bigger recurrent exercises, but far from the only one. Multiple giant exercises happened every year. All across Western Europe. Very little of it simulated (no virtual computer network yet existed to do that). Actual Corps, Brigades & Divisions out physically maneuvering on the civilian landscape. Rehearsing their actual wartime defenses & counterattacks in free play against equivalent sized "enemy" forces. The gun fire was simulated, but the troops and war machinery were not.
Meaning tanks & APCs rolling through peoples yards, fences, and town streets. Accidentally crushing parked cars or clipping the walls of houses. Miles long traffic jams of military convoys. Forests filled with hidden artillery emplacements and camouflaged troops & armor. Fleets of ships, airplanes, and trains moving the actual sinews of war from the USA to European ports/airheads... and then into the exercise landscape. From Norway, UK, & the North Sea to the Warsaw Pact Frontier to the Bavarian Alps. Gargantuan.
None of it conducted inside of actual military training grounds.
I participated in those European exercises for years.
A coupla dozen high speed guys and a few helicopters firing blanks over a coupla buildings/streets for a half hour or so? Meh.