I would say because the 8mm bullet was never that popular here in America, so it only makes sense that it would not catch on, though it is rather disappointing, because it is an efficient cartridge.
I wish more long range bullets were made in the 8mm, it would be another great option for elk and the like before stepping all the way up from a .308 to a .338....my father has an 8mm-06 built on a mauser action that shoots great and flat out kills things. 180 grain NBT's at 2950. But in the 325 wsm case or possibly a 325 Winchester magnum wildcat or other larger cartridge, a sleek high bc 220-250 would be an awesome long range elk hammer.