There's no good reason for them to be on the road. Consider the following:
They're extremely loud and cause noise pollution
They're very dangerous on the road and have high accident rates
They're bad for the environment and cause air pollution
They're extremely inefficient as they can only carry 1-2 people max
They can't carry cargo
They're dangerous for pedestrians
They're very demanding to operate
They're virtually useless in the winter when there's snow, ice, and hail
The people who tend to drive them tend to be assholes who don't respect road laws
People complain about cars all the time, and while our car dependency is definitely a big issue that we need to address, cars still have a lot utility. Motorcycles on the other hand? Not really. I think getting rid of them once and for all is good way to immediately make our roads safer, simplify traffic, and open up a pathway to move away from cars.