Japanese people all have a long family history of living inside of the same flavor of society they live in now.
Outsiders might on average have a harder time coping with the expectations of Japanese society, because they don’t share this multigenerational experience in the society. The degree to which they will have a hard time likely depends on how similar the society their own multigenerational experience comes from is to Japanese society, along the most relevant behavioral dimensions.
It’s not that they are bad people, they just have a harder time with the system. We can’t really blame them for that, can we? While at the same time, it is a valid reason to not let them in.