I believe that perception is key, no-one goes to an art museum to see mouldy artwork on rotted canvasses so why would the public want to see dilapidated military vehicles that are falling apart in a military museum? I have travelled extensively in Europe (on my own dime) and the national museums over there have dropped this antiquated display method in favour of restored vehicles which I feel shows a respect for the artefacts. This respect is in turn passed on to the viewing public who realize that they are not looking at unkempt metal but respected historic items.
No rusty junk in the Panzer Museum in Munster.