I think alot of shelties are not natural retrieves. They get the chase part but the bring back part is lost on them and need to be taught.
Justice is a natural retriever. I throw, he runs, grabs, brings back. Point to an object and he would go get it. I never had to teach him to retrieve at all, even as a small baby puppy. I just pointed and he did it. I have since found out that it very rare indeed.
Diva, Pike, Bock and Grizz, had the chase and grab but bring back part I had to teach it.
Ember has the you threw it, you go get it attitude. I did teach her to retrieve and she is very good at a formal obedience retrieve. But she will not retrieve anything that she has not been taught to retrieve ie dumbbell, gloves. She doesn't care to play with balls or other toys.
All the above dogs except Grizz come from several genrations of obedience dogs so even selecting dogs who are more willing to retrieve and work(higher drive). Only 1 was a natural.