@Chara nailed it. I love the high density flower plantings, legit fields of quality smokeable plants just stanking!!!
The density you use depends on what you are trying to achieve and probably the cost of seed. Seed is much cheaper in Europe because of decades more experience. Hemp is also just a rotational (mostly) fiber crop in Europe, they didn’t have high value CBD plantings until relatively recently. They also have different pesticide restrictions that likely make the weed suppression from high densities more valuable and adds value to following crops.The US suffers from varieties not bred for our climate, so growers play around with recommendations from Europe to find what works best here.