Sure, but in Europe you can drive for 30 hours passing from a metropolitan area to another. You probably don't know what I mean but the population of london is slightly less than the entire population of michigan. Italy alone has a population that is one fifth of the ENTIRE US.
Italy is about the size of michigan (300vs250km²) but has about 6 times the population (58Mio vs 10Mio). The population density of Italy is 5 times as high.
That's only if you include Russia (145 million) and Turkey (85 million). You only include those countries in "Europe" when you want to. That's like the US including CA and MX in its population just because they're nearby.
Okay, countries just within the European Union have a population of 450mln. Also, we were talking about demographics - Europe vs United States. Everyone includes those countries.