They lack any meaningful design in comparison to other currencies, since all denominations stick to mainly black and white designs with slight hints of color as they’ve remained the same for a long time. Why won’t USD switch to Polymer bills (it was first unveiled in Australia) like they’ve done in the UK or UAE for example.
Because only old people who suffer death of personality when witnessing anything unfamiliar even use cash anymore. If you made plastic money that vote Satan Q. Hitler in as president just to self-soothe.