Why do injuries happen frequently for people who do not exercise?

If you don't exercise your body won't function/perform as well as a healthy body should. If you don't exercise the way it won't perform is that it'll take damage easier then if a healthy body took damage. To conclude, your bones aren't as strong if you don't exercise so your body can't fight back the injury taken in. Hope this helps!

Explanation:

Injuries happen frequently for people who do not exercise because they are not strengthening their bones and muscles.

Explanation:

If they do not exercise, their muscles and bones are not in constant movement, stretching and/or training. They become hard and stiff, making any sudden or hard movement to stretch it suddenly injuring the person by either having a broken bone, sprain or bruises on themselves.