I frankly dislike this kind of question. The problem is that not only is the answer frequently not known, but worse, people love to make up pet theories about the reasons and post them as if they were truth. Then others see them, think "oh, this makes sense" and upvote. It doesn't matter if this is the real reason, people seem to love to participate in this myth building without giving it a second thought. UX is especially plagued by these questions.
If you are to ask why a practice works, then this is a good question and should be accepted. But if your question is of the type Why did a doctor do X and not Y in a case where both X and Y would have been feasible... well, we have no idea why. It could have been a hunch of his, him having a contract with the lab which does X, or he learning in med school a lot about X and very little about Y, or any other of a thousand reasons. But nobody here can tell you. Nevertheless, there will be a bunch of people who will tell you their guess, presenting it as truth.
Even when the question is on the tendency of choosing a practice in a population of doctors, it doesn't work well. Sure, these are interesting questions. But they would need sufficient historical research before they can be answered. And the answer is often boring: "This is how the first guy did it and it became so widespread it got to be a quasi standard, and from then on, nobody had the reason to change something that works, even if a later option would have been marginally better". But the votes tend to go to the people who offer clever ideas, even when they are untrue.
Maybe this site could do better than UX in this regard, because of the culture of not-upvoting answers without references, and not offering simple guesses as answers. But in this case, I don't think you'll even get answers. The real ones are hard to find and not very useful anyway.