Scooters are an accepted form of economical transportation in Europe. It's not simply "car vs scooter", or filtering versus being stuck in traffic. Piaggio established a common standard 60+ years ago, and it has stuck. Parking is less of a problem, petrol cost is lower, purchase price is lower and a huge portion of the population is daily riders, so the product is well positioned as a "normal" choice. If Piaggio pulled out of the market, others would fill the gap. What goes on over here, as I have said above is product differentiation to try to tilt sales towards your own product. It became quite clear a few years back that Europeans are pretty savvy about scooters, and the cheap Chinese crap never gained traction. (Sound like the Yugo in the US?) Scooters are "serious business" here.
Getting Americans to make a serious shift to scooters as a daily ride, even where the weather is accommodating, would require a significant culture shift. Where Europeans have 60+ years incorporating the scooter into everyday life in all segments of the population, Americans have that much ingrained experience identifying with their automobiles. PTWs reside in another category altogether in the US.