It is extremely hard on the kitten when it gets returned to the breeder. They may be glad to be back to what seems like a familiar setting, but it isn’t like before. They are immediately put into isolation. They are given a bath. They are taken to the Vet for a thorough check-up, if needed, undergo a spay/neuter surgery.
The other cats in the home may now react to the kitten in an aggressive way (as it is no longer familiar to them, and their scent has changed.)
When the kitten gets rehomed again, it has to adjust to yet another new environment.
Hence, it is extremely important for us to find our kittens permanent and stable homes, willing to make a life long commitment just as one would for a child.