yeah and -- the program puppies are also going to go to handlers who may or may not be very good at handling, good at timing, good at all manner of things. it is a very, very different audience. and some of that is that you're deliberately aiming for good enough with minimal support and training for anyone to handle, including often people who are literally not capable of getting timing down super well (motor disabilities will do that to you, as will anything that affects coordination or dissociation or any of a number of other things). you are aiming to do this very hard thing by just throwing sheer numbers of dogs at it, too: puppy raisers may or may not know what the hell they are doing (no shade, raising puppies is hard), and then you have a big wrenching stress of transitioning from puppy home to training kennel to placement, and then you have whether or not the dog decides at some point along the way that it isn't worth it, fuck this noise.
lots of working dogs absolutely could not handle this kind of handling. it is frankly quite impressive that so many retrievers pull it off so effectively, and IMO the fact that they do says powerful things about their biddability and drive in the face of a rough environment, partly as a function of their ability to hold up under historically rough handling in gundog kennels.
you do see some similar things in other working dogs, too; some of the trainers I have seen selling finished herding dogs talk about this, about creating dogs that are deliberately less sensitive and less fine-tuned who will do well with an indifferent handler vs keeping more sensitive dogs back for experienced handlers.
but... in a lot of ways, programs are designed around the idea of dogs as essentially fungible components in a huge system that will be doing a lot of work for indifferent reward. it is genuinely really impressive that so many dogs move through service programs and turn out as functional dogs as it is. but there's just straight up not a ton of comparison between program needs and owner-trainer needs, IMO: programs run on volume of dogs, and they often do wash for things an owner-trainer could benefit from taking the time to fix and rehab because programs always have more dogs to choose from.