I think since the introduction of euro and Schengen the percentage of eu-citizens who never been outside their country has dropped close to zero. Also think the percentage of eu-citizens who has never left eu is smaller than us-citizens leaving the us is. States are big yes, but the difference between states is smaller which means it makes less sense to travel ‘abroad’.
Too bad nobody saw this coming, they could have made a great movie about this 10 years ago.