Here is one reason why…

Everyone’s luck runs out eventually. When that happens to you, you may find yourself and your loved ones at risk from a malicious or mindless threat. If this situation is something that you can do something to overcome, then you ought to be in the best possible shape you can be to overcome it. You may not ever be as strong as Thor or as smart as Sherlock. But at least if you know that you are as strong and smart as you can be, then whatever the outcome of your encounter with doom, you could not have done anything more. And if you get any enjoyment from the preparation then all the better for you.