
Could be, as certainly most horse owners don't keep their horses for life, and there is less attachment than to pets who live in the house.
On the other hand I know breeders who will home bitches and dogs (even champions) that have made their contribution to the line and the breed feeling that they deserve the extra attention as they get older of being the one and only adored pet, leaving space for the breeder to carry on their passion for the continuance and development of their breed line.
Some peoples priorities lie with the individual dog, some others with their line and the breed as a whole.
I know if I was able to let my girls go I would have developed my line and knowledge more, but I have never been able to let one go once it has been kept past the baby pup stage.
This of course means If what I keep isn't very good I won't make any headway for many years, but I am still young enough for that not to be to much of an issue, and I am not in such a hurry.