On bikes, you can't go over a certain power/size for a period after your test. There is also an age stepped restriction on learning to ride big bikes.
At the end of the day, bikes and cars are exciting to most young lads. Its been driven into them that fast cars and bikes are cool, they don't see cars as transport like young girls(in the majority you feminists!
) do, they see them as some expression of their macho image. Its this fundamental aspect of car ownership that skews the figures so much, nowt to do with driving ability.