>Why are they always ignored in these threads? Is this an American thing?

I don't know but Vespa-type scooters are very uncommon in the US. Motorcycles are less rare but are widely considered (with some justification) to be dangerous as a form of transportation. (It doesn't help that there are some crazy motorcyclists out there though of course many aren't.)

May have something to do with the type of road infrastructure and traffic, or just custom, but don't really know.