Why do aircraft on a junk yard have blind windows (e.g. German "Landshut")? Today I saw a picture of the “Landshut” (named after a German city, pronounced lund's hoot, not Land shut). The aircraft was hijacked in 1977 and now rusts at the airport of Fortaleza (Brazil) since 2008. German enthusiasts wanted to transfer the plane back to Germany as it somehow and sadly became part of German history, and the German government intends to do so as well.

(http://hessenschau.de/panorama/landshut-104~_t-1488105510615_v-16to9.jpg)
(Source)
I noticed the windows are blind. In an answer to an other question here I can also see a “retired” plane and Peter K. mentions the blind windows in a comment. This gave me the impression that all “retired” planes have blind windows.
Do the windows get blind simply because the planes are left on their own for years and wind, sun, etc. make them blind or are they made blind on purpose? If so, which purpose?

Addendum
After reading the good answers, I reviewed the video I already linked. This screenshot:

(Source: tagesthemen from Feb 23, 2017, 22:15h (German TV news magazine))
shows the cabin of the “Landshut” and it's clearly visible that the interior is removed and the windows are blanked from the inside and covered with grey foil. I just wanted to share this image.
taken from Business jet news 


  For outside storage, cover windows and recognition/strobe lights with barrier material and pay attention to atmospheric conditions, as humidity will accelerate corrosion. Make sure all control locks or control column gust locks are installed to prevent movement of flight control surfaces.
  (emphasis mine)


One reason to protect the inside fabrics, plastics etc from the effects of discolouration from sunlight, as well as inhibit biological growth. Also without the coverings the temperature inside the aircraft will be significantly higher on sunny days see Desert Usa


  [without protection] the interior could quickly heat up to 200 degrees Fahrenheit during hot summer days