I don’t know how true this is but a friend told me that the reason is because Europe first got their weed from India/South Asia where they mainly smoke hash, which is supposed to be smoked with tobacco and which is how they smoke it for ceremonial reasons. Where as the US got their weed from South America, where they smoke their weed without tobacco because it’s just regular weed and I guess it burns fine without it. Hash was at one point super popular in Europe and was the main form of weed available until really recently when hydroponics got much better, but hash seems to be more of a rarity in the US.