Not an expert on Oregonian law, but my theory is that Oregon's motor vehicle law references the federal NHTSA regulations, and Kei vehicles laughably don't meet them (exterior lighting, crash performance, theft resistance, emissions, and so on).
An owner might be able to use it as an off-road vehicle only (no title, no tag, with maybe only comprehensive insurance), but that's not the point of buying one for a lot of owners.
NHTSA has a 25-year rule that allows a car old than 25 years to be imported without those considerations. You can definitely import them legally in Texas. I find it funny that we disallow these new smaller trucks, but we allow folks to jack up the suspension on an already large American truck 24 inches, install a grille guard, and it's still considered legal.
They are also huge offenders! At least in Los Angeles.
A pet project of @FilmThePoliceLA is filming & posting videos of cops’ personal vehicles with illegal modifications. He calls them out directly if he sees them, they never have any reasonable response.
...or when my local inspection station, and the cops, don't even blink at a Ford 350 with a huge-ass lift kit, mud tires that don't grip for shit and extend inches (or more) past the fenders which is insanely dangerous, a front bumper that has been replaced with a thick sheetmetal version, and the rear plate is covered by a tinted, a glossy plate cover that makes the plate virtually impossible to read, and the cherry on the pie: a "DPF delete" which means the guy is belching diesel particulate everywhere he goes.
It's funny you mention that. The other day I was out on mine on a coastal highway here, waving at a bunch of other people doing the same thing, and thinking "If someone invented these today there's no way they'd let them on the road."
I'll play devil's advocate on this one -- most motorcycles sold today will do 125mph and the Kei trucks I'm familiar with cruise at around 55mph reliably (some may technically go up to 65mph if you sit there redlining). I'd guess some concern comes from holding up single-lane traffic. And this is coming from someone who loves the Kei trucks in rural New Hampshire, but I have been stuck behind them before too.
Also motorcycles are a part of Americana history (there's no "Easy Rider" where two guys ride a Kei truck cross-country). I'm not at all sure motorcycles would be allowed if they just started popping up 10 years ago in the US, we've gotten risk averse in recent times.
A single lane road with a speed limit above 55 but no passing zones is a strange beast indeed. Don't think I've ever seen one. Also plenty of construction and farm equipment is street legal despite some of them not being able to break 25mph.
As always, it's a speed limit, not a speed target. Overtaking lanes exist for a reason. As long as someone isn't going unreasonably below the speed limit (which is also unsafe), then it's completely fine.
Dark take with just enough data to make it a talking point: motorcycles allow the rider to fly off and die from a traumatic brain injury, while preserving their organs.
If you’re crushed in a Kei car they probably won’t be able to salvage much.
An owner might be able to use it as an off-road vehicle only (no title, no tag, with maybe only comprehensive insurance), but that's not the point of buying one for a lot of owners.