The difference is that Asia has had intense centralized agricultural economies for something like 6,000+ years while (north/west) Europe was primarily pastoral until around the Roman empire.
Agriculture spread throughout Europe during the Neolithic, like the rest of the Mediterranean basin (and possibly towards India), and brought along massive deforestation and demographic growth. Those were deeply agriculture-centric societies far before the Indo-Europeans came around, not even mentioning Romans.
And in what parallel universe agriculture was centralized in Asia in 4000 BC ?
The big advantage of Asia was double or even triple crops.
It took a long time for agriculture to spread. Crops that work in a Mediterranean climate do not work in Northern Europe. You have to breed new varieties. That can take hundreds to thousands of years. Heck, it’s still hard to grow certain kinds of fruit up here in the rainy parts of Oregon and we know how genetics and inheritance work.
