Obligations flow from without: from kin, community, and the commands of the ancestors. Morality, if it is to bind at all, must come from outside the moral agent.
What follows from thrownness is inherited obligations, giving us the folkish moral form: heteronomy. The Greek term means "law from another." In folkish society, obligations flow from without: from kin, from the community, and ultimately from tradition, the commands of the ancestors.
Morality, by definition, must come from without. If one can bind oneself, one can just as easily unbind oneself. If morality depends on the will of the moral agent, then morality prescribes nothing. Without heteronomy, duty vanishes into thin air.
The axial rebellion against authority resulted in the discarding of heteronomy and the turn to autonomy, law interpreted by the individual. But once you are in a position to interpret or judge the law, you effectively are the law, making individual conscience the final court of appeal and collapsing duty into preference.
Folkishness rejects self-legislation and affirms heteronomy as the only form morality can take if it is to prescribe anything at all.