It didn't get "lost," the main issue was (and still is) the lack of available commercial ammunition. Ed Johnson couldn't get any major ammunition manufacturer to produce ammunition. Ed tried to make it himself but couldn't produce it fast enough. He had quality problems with several smaller producers, and due to the lack of ammunition orders didn't come in fast enough to stay in business. The cartridge is a good one, but the ammunition problem hasn't gotten any better. Even if today a guy tried to re-introduce the carbine it suffers from the same issue, lack of ammunition. And rifles where one has to "roll his own" have a very small market.