I had a similar thought today about e-bikes and other micro vehicles; why do we allow e-bikes to ride on the road, but ban small trucks and tuk-tuks like this one?
Because e-bikes are hard to differentiate from pedal bikes legally and we haven't done it yet, and if you advocated banning bicycles on roads I wouldn't like you very much.
A better comparison, as far as flowing with traffic, is a moped (i.e. Honda Navi, top speed 55mph) rather than a motorcycle (i.e. Suzuki SV650, top speed 130mph).
I had to look it up myself, not being sure, but "the Navi isn’t freeway-legal in many states" [0]
So probably allowing them on city streets but not highways is what I would propose, to answer your question. I don't think banning them altogether is right (for the Kei truck or Navi) since micromobility has all sorts of benefits where it fits.
Motorcycles are much less safe when compared to this truck. Would you also ban them, or do they receive an arbitrary exception?