The household income part is telling. Makes me think this is based on identity politics rather than polical or economic scale.

Lower income people and higher income people are both in general more happy/less stressed than middle income people.

Poor people generally have less debt and more free time than middle income people who generally live way beyond their means.

Seeing how the conservative low income on this scale scores about the liberal middle income suggests the scale is based on identity politics.

Regarding identity politics conservatives are actually the centre of the scale.

With regressive identity politics and liberal identity politics on either side of the scale