You said "americans avoid two wheeled vehicles for no reason".
They have cars anyway so they use them.
The reason they need cars is because it gets cold, there are highways that go fast and it's dangerous and illegal to take young kids or more than one kid on a scooter. This is not complicated.
Also the honda scoopy and yamaha scooters are 115cc and can't get up to american highway speeds. In Thailand it isn't even legal to drive scooters or even motorcycles on their highways.
Maybe you should go on holiday to Vietnam in the winter, you might realize there is no snow in Vietnam.
Americans usually need a car anyway so they already have one.
It has everything to do with your refutation of that claim, however.
My actual implicit claim is that there appears to be a degree of truth in the idea that US residents have a cultural aversion to two-wheeled transport that extends beyond the justifications you proffered to dismiss the claim.
No there isn't. People have jobs to go to and there isn't much public transportation, it gets cold, snows and people need to use the highways. People need to have a car so they already have a car and that's why scooters are usually something people buy for fun and not neccesity.
People in developed economies shouldn't be carrying around sofas on the backs of mopeds as they do in Vietnam, but it should be reasonable enough to deliver a pizza on one where the weather allows in the USA.
FWIW: I'm very much a car guy.