The reason you don't see the Kei vehicles in the US and Canada is entirely down to the shitty Ford F150/250/350, Jeep Grand Cherokee, Dodge Ram 1500, and their supersized moronic vehicles like the Hummer, along with regular 5th wheels can crush these Kei cars like they were a beer can. This is ALSO the reason why American and Canadian Light Rail sucks so much, because the light rail has to be bogged down with weight so they can withstand being t-boned by a moron driving a Hummer or a 5th wheel.
For actual fact "tiny" anything, be it tiny cars, tiny trucks or tiny homes, is a scam. The reason they are small is because the person selling it to you is a grifter. Instead of getting a proper sized vehicle or home that you can actually use, and survive using. A tiny car/truck is crushed like beer can in most accidents with other US vehicles, and a tiny home is a death sentence on you should it ever catch fire. If you aren't living in at least 500sq ft of space, you've been scammed and you will die in a fire because there won't be any escape. A tiny car has no hope in hell of being survivable in the US unless you drive strictly on the city roads and not the highway/freeway.
Another reason why you won't see Kei cars any time soon is a unique geographical feature of North America that Japan doesn't get. High winds. High winds + snow, your car is going to end up in the ditch. A Kei car not only ends up in the ditch, but lacks the survivability when it's hit by another car during snow. High winds like in British Columbia and Washington year round on the highways, or in Florida during tornado/hurricane season will even push the small American and European cars off the road.
Like yes, some of the lobbying is why you won't see it, but they aren't wrong. If you've watched any people record themselves driving in Japan, you'd also realize Japanese roads are not made for American sized cars and trucks to begin with. This is why the Kei car can be a thing, and you're only really taking a risk with your life if you dare take it down some unpaved roads, much like in the US and Canada. But in the US and Canada, a logging road is usually something a regular car can tolerate without significant risk to the driver. You're better off driving a Jeep Cherokee or another larger SUV down a logging road because you want clearance over rocks. American roads were designed for the "horse and buggy" size, where as many european and asian roads were designed around walking, which is why their cars are often smaller. Bigger cars can not fit down roads designed for the width of a single horse.
Another thing, which you may only realize from playing the game "Initial D" is that Japanese roads are extra curvy, much like roads in BC, Washington, Oregon and Alaska. How we solve this in North America is by making the roads over-sized so people don't fly off the corners. Japan? nope, regular drivers don't slow down. In North America, if you don't slow down before you take a corner or a hairpin turn, you are likely flying off the highway and down a ravine.