>>279875587
>A dragon girl is pure wish fullfillment to make a dragon a fuckable companion for the MC.
That makes sense, honestly I figured it was when the Arifureta MC got his dragongirl wife by shoving a metal rod up her ass. A lot of these girls also start out as enemies in their dragon form, before being defeated with the "Twist" of them turning into a human form after. Easy way to kill two birds with one stone by having a big enemy for the MC to show off on and then get a free girl out of it too.