But nobody has 4 + 4? The traditional system was in Europe 5 + 3, now we mostly have 3/4 + 2 + 3 (Europe) or 3 + 1 + 3 (UK/Ireland).

I don't have a lot of experience with the US system, but from my experience after 3/4 years newly minted postgrads are probably not yet ready to knowingly commit to 5 years of specialised training. European-style MA/MSc's often feel "useless" because they actually help people switch course and find a new footing. However, good master's programmes are either flexible enough for advanced students to take more specialised modules or have high demands to begin with.