Why keep the doors open for aircraft in boneyards?
Scrapped aircraft are often cannibalized for parts, it's possible that the parts that were needed from this specific aircraft were the doors.



The photo provided in the question points to Victorville  boneyard, and some detective work using the partially visible registration indicates the 747 in the picture to be G-BNLU. Some digging on the reg shows us it was withdrawn in 2014


  Withdrawn British Airways Boeing 747-436 G-BNLU positioned Cardiff-Wales – Victorville this morning as BA9156.


It seems that at various times there have been 7 BA 747's stored at victorville


  747-400s; G-BNLA, B, C, D, G, H, U


And at least one has visited Victorville for a refit


  I was on airliners.net reading some posts/threads and I read one: G-BNLV is back from the desert!! 


(Both above quotes from this thread)

Which lends weight to my original assertion of cannibalization, however nothing concrete as to whether U provided new doors to V.