How is it possible that I'm losing my hair even though I have a lot of body hair elsewhere (e.g., on my chest)?

Hair loss on the scalp and excessive body hair are not mutually exclusive. This is often caused by the hair follicles reacting differently to hormones (especially DHT): while the hair on the scalp reacts sensitively and thins out, body hair may actually grow more vigorously. This genetically determined sensitivity affects only certain areas of the hair follicles and is a typical pattern seen in hormone-related hair loss.