it seems to me the cubes made their way into kits when there was not really much else to be had in the way of a survival "food".
in the 50's when kits really got started there were no power bars or energy gups on the market.if you were lucky surplus military life boat or bail out kits could be broken down for the compact rations in them.i take the larger bouillon cubes on canoe trips and every few years boil one up on a nasty wet and cold day to go with a MRE cracker and like it was said they can be a comfort food if you happen to have developed a taste for them.the hassle with them is of course you need to "cook" them for best results and that means a pot,water and fire all of those are a survival problems in themselves.
sorry,another 1:30am ramble.