These aircraft were made under wartime conditions in the open or in unqualified factories and with ersatz materials by unqualified people including prisoners. Not made to last.
To blame the museum now for not having it airworthy is a bit unfair. I consider it a great fact that they have kept it and saved it when post-wartime research was terminated and those former high tech aicraft were abandonded and considered junk. No surprise that those remains age after all those years.