The obstinacy of persons in charge of acquisitions for large military and para-military organizations rears its head WAY to many times as the reason for hanging on to obsolescent weapons systems, even in the face of proof of superiority of other systems. Witness the long run of the Lee-Enfield and the bolt-action Mauser. Even after M1 Garands became prevalent on the battlefield, the Germans clung to the MP-40 and Kar 98K, thinking that the MG-34s & MG-42s would cure all ills. They eventually saw the folly, and fielded the GEW-43 & StG-44, but far too late in the game to make much difference. The Brits remained clueless until after the Korean conflict, but then surpassed the U.S. by adopting the FN-FAL rifle types, while the U.S. hung on the M1 until 1962, when it was replaced by the excellent M14.
I don't like to think about what happened after that, so I'll stop here.