Well, because of the various versions of the 5α-R enzyme, one particular version known as 5α-R1 is expressed in the fetal scalp. Like many genetic hormonal factors – including your muscle insertions, bone size and even your height – this hair-loss sensitivity is predetermined by your genetic makeup in the womb long before you are even considered a human being.
So, you’re welcome to blame good ol’ mum and dad (or more specifically your mother’s father) for whatever hair-loss gains that are bestowed upon you, regardless of what compounds you are considering using. But unfortunately, if it’s going to happen… it’s gonna happen. You need Test and DHT in your system, so the ever-present hair-loss androgen will always be increased with Tren usage (as said the Tren itself won’t do it directly), and you are asking for permanent trouble by blocking 5α-R and lowering DHT. Your best bet here is to utilise a localised site blocker, normally found in selected shampoo treatments, to prevent 5α-R androgenic activity exclusively on the scalp.