Perhaps in Europe things are different.
Exactly. They’re more than capable, physically, of being adopted at eight weeks, but many if not most puppies don’t make the emotional/psychological shift until nine weeks. I.e.: some (I don’t know the percentage) will grieve the loss of their family at eight weeks; at nine weeks, they are eager to leave the litter and bond with their new primary humans. I have see this with my own eyes. It’s horrible to watch a puppy get depressed over losing his mother and sibs. It happens at eight weeks, but never at nine.
I always thought that was the norm. Our dogs, a toy breed, were 12 weeks before the breeder started selling them. The one came to us at 15-16 weeks. Her brother left at 15 weeks, was returned to the breeder and came to us at about five months. It took them a couple days to bond with each other, but no time at all to bond with the humans in the house.