I don't think I can participate in this poll because by choosing one, I feel like it would be saying the others are unimportant. "All of the above" and then some would be my answer.
PERHAPS my answer would be to be patient and do one's research and go to Glider Gossip & Gliderpedia for answers.
OR perhaps question everything a mill breeder has told you and see if it sounds like their reasons are influenced by money (aka being cheap or trying to make a quick buck) or inspired by a need for healthy gliders.
OR perhaps to just be patient and not get overwhelmed. Take one day at a time.