Don't know about the USA, but in my country (New Zealand) you could not
legally fly a military warbird as a civilian aircraft until about the
mid-1970s.
Those few ex-military aircraft that were used were either based on an
original civilian design (e.g. C-47, L-4 Cub) or were operated by
commercial operators (such as airlines) that had enough financial
resources to put the design through the full civil aviation assessment
process.
Many of the higher performance military machines had construction or
flight characteristics that were not acceptable in a civilian
environment. An example of this was the de Havilland Mosquito, which had
a 'dead man's gap' - an engine failure just after lift-off and before
the aircraft attained a certain speed just could not be controlled, and
would always result in an uncontrollable roll towards the dead engine
and a crash.
Peter

wrote:
Didn't ANYBODY after WW2 have the love of airplanes and the foresight
to buy at least one military airplane, especially since they were so
cheap? What were they thinking?! Did they not see the value of these
planes for future generations? Why didn't some civilians simply buy a
B-17 for $700 and park it in their yard? Land is cheap in rural areas.
These airplanes are so precious to me. I have loved the glory of ww2
fighters and bombers since the earliest childhood.