dittos here....there are several variables. Distance has to be a factor, in addition to trust and also veterinary care.
Bottom line is that decision is up to the individual breeder, since they are the one taking the biggest risk. There is a certain amount of inconvenience to the guardian home, in the breeding absences, or stud services, etc. but the breeder has to be comfortable that their dog, who is also an investment is well-cared for, and in a safe place.