Beacause there is not DHT resistant or DHT susceptible hair. Every hair is the same. You probably haven't heard about those two words - calcification and fibrosis which block the blood flow to the balding follicles and that's why they grow thinner. The follicles don't receive the necessary levels of oxygen and nutrients and they are starving. Don't worry. You can regrow full head of hair even if you were slick bald for a long time. The hair doesn't die. It just becomes small velus hair which is barely visible to the naked eye.
The DHT causes hair loss by signaling TGF-B1 and this lead to arterial calcification and perifollicular fibrosis over time. It happens on top of the head because the chronic involuntary contractions of the surrounding muscles(frontalis,occipitalis, temporalis) pull up constantly on the galea tightening it and increasing inflammation and androgen metabolism. The location of these muscles matches exactly the Norwood 7 horseshoe.
If you compare someone with shaved head who still has hair versus someone who is bald you will notice the stiff and thick layer of skin on the bald scalp.
You can recover from androgenetic alopecia. You just need regimen. Go to the section "Success stories" and see what people have done.