OK. So it's in a military base. Probably it's easier to keep all those tanks in working order that way, with trained personnel to service them...
...seriously, how difficult would it be to put a
fence between the military base proper and the museum grounds, and
not put "military secrets" on public display, or at least keep the latest developments (as opposed to "regular" equioment which everybody has seen and which the foreign powers have had access to ages ago) in a base which does not have a museum? Oh, they want to show off their latest hardware to fellow citizens... as if those same secrets could not be leaked by the supposedly loyal natives?
It's like the US Air Force Museum would be located within Area 51, but US citizens could still pass freely.