I Found Part of The Answer
I found an answer in a book titled “Bullets By the Billions” by Wesley W. Stout. It was about how Chrysler Corporation converted to the war effort and goes into detail about brass vs. steel cases, primers, etc. and the efforts required. I found an online copy and am reading it. Anyway, here is what it says about repacking:
“Employment had reached a peak of 12,655 in September, 1943. It was down to 7,951 by early January, reached a low of 2,401 May 31, 1944. These two thousand stayed on for the repacking of a billion and a half rounds of .45 and .30 ammunition between then and October.
BULLETS SEALED IN CANS
These cartridges had been packed originally by Chrysler and other makers in containers of double-dipped, heavy, waxed paper enclosed in heavy wooden boxes. Ample protection in the past and in the fighting in Africa and Italy, the pack failed to stand up in the South Pacific and by midsummer of 1943 General MacArthur was asking for a better one. Ordnance gave Evansville an engineering project to develop such a pack, out of which grew a heavy gauge can made by the American Can Co., hermetically sealed, opened with a turn key like a can of corned beef, and capable of being resealed with scotch tape if all the contents should not be used at first opening.” (Pages 46, 47)
“General Kirk in May. 1945, told Mr. Jacobsen that the repackaging program was the greatest single contribution made to the war by the Evansville arsenal, exceeding even its successful production of steel cases.” (Page 49)
So, I don't know why the flaps were glued but now I know why they were repacked.