Because it is important.

The more egalitarian countries show more differentiation across career choices than less egalitarian ones. I.e. men show a greater prefence for thing based careers and women show a greater prefence for people based careers.

If you've ever watched kids playing you'll realise how self evident it is, from a very early age before kids are remotely aware of cultural norms.

This flies in the face of all predictions that roles of sex are purely cultural.