Scalp tension, mainly due to tight muscles surrounding galea and less blood PRESSURE to get through ( yes the scalp has loads of blood if you cut it, this disproves nothing ) inflammation then DHT then hair loss follow in that order.
So basically your galea is injured and inflamed under the skin as it's being pulled down by tight muscles around the sides. There is less blood pressure on route to galea hair follicles malloclusion may play a part here also.
Like anywhere on the body, DHT arrives at the site of inflammation. It's a simple google to confirm this well studied fact. it's no different with the scalp, hence hair loss.
At this stage I'm staggered most people think it's down to genetics, unless of course that's the genetics of having a huge galea, poor posture, mouth breather, tight temporalis or whatever is the main culprit for someone's tight scalp.
But the arguement that some people have some specific hair that is prone to attack from DHT, is 'genetics' is bonkers. It doesn't half make a lot of money though.