Well, the older puppies get, the more WORK they are! Mom isn't cleaning up after them anymore, they are rambunctious, they make a mess of their food, they pee and poo ... a LOT. They are a lot of work for sure.
Some breeders are more than ready to get them out of their house and into new homes as soon as they can! Less work for them! The longer they keep them, the lower their profits sink as they buy more puppy food, puppy pads, and invest a lot of time in feeding them and cleaning up after them.
An unethical or naive breeder wants to get rid of those puppies as soon as they can. It is NOT in the best interest of the puppy. It is selfishness on the part of the breeder.
"Having heard all of this, you may choose to look the other way.....
but you can never say again that you did not know." William Wilberforce 1759-1833