I will agree to that. It's very hard to maintain a line without 1) a lot of individuals to select from, and 2) enough land/space to keep them.
Sometimes maintaining a line takes a few breeding steps, where you have to keep individuals from a few different matings, and you have to have the room to keep the dogs of each generation ... which (I agree) is not feasable for most folks in this day and age. So well said.