Because it doesn’t have any benefits. Hair loss, loss of elastin, upregulation of sebaceous glands (meaning acne). It’s not anabolic (metabolised by 3-alpha-hydroxysteroid reductase in muscle tissue (non-androgenic tissue)). There isn’t a good reason to have it circulating your body at all.
Been on 2.5mg Dut for over a year. No issues at all. No regrets being on. I knew sides were an meme by r/tressless schizos so I didn’t bother with 0.5mg. 2.5mg vs 0.5mg serum levels are practically the same anyway (nuked), just scalp DHT there’s an extra 30% suppression.