Those countries are more demographically/culturally uniform and are higher trust societies. Even Bernie Sanders admits this is necessary for large social programs.
There is a vein of thinking that “diversity causes division” in the United States and this undermines our political willingness to create effective universal safety net programs.
High trust vs low trust societies tend toward egalitarian vs clannish communities respectively.
Which is a strange thing to claim because e.g. in Germany, Protestants and Catholics "coexist in the successful European model", whatever that means. Claims of "can only thrive" are trivially refuted by counterexamples.
What does that even mean?