Probably be a lot harder now we have no Japanses manufacturers in the sport, KK got his chance through Toyota and very nearly didnt have one once they pulled out.
I think a lot has to do with champtions, when theres a Driver from a certain country, lets use Emerson Fittipaldi as an example, who comes in and wins things then their country takes notice. This in turn leads to young children wanting to emulate this driver and they take interest in F1 (or whichever type of racing) and so that country produces racers, like Nelson Piquet or Senna who influence further children.
Ofcourse Countries within Europe have always been racing, Germans, Brits, French etc so theres always a large pool of talent from these countries and the best can be filtered out due to the amount of racing categories that are around.
Regarding Italians, perhaps they choose to race on 2 wheels as they’ve had quite a few champions on bikes like Rossi, Agostini who are/were real forces in the sport.