Oh so you mean the magic does it? Then why would they have an alternate way to reproduce? If the magic works the dicks, they could just have baby vampires flying around the normal way, and the very concept of vampire would be pointless, and zombies could have hard ons as well, and a new category of porn would come out of it... Though werewolves don't really need the " contamination" process since they are basically living creatures and they can just fuck and have babies... Oh and what about ghouls? Are they even considered as supernatural creatures with reproductive abilities?
Nah that theory is not satisfying ヽ(`Д´)ノ
Ahhhh look what you've done, you added more questions xD
How do vampires have erections without a beating heart pumping blood through their body?
Yes i know it's a stupid and pointless question, but i still have hope that somebody, somewhere, at some time, thought about it and imagined a functional theory.