Why is the sin nature inherited?

[Ryantology]

I know I did not say this because my whole 'orgins' theory is based on the idea God knew when the fall was going to be and planned Adam and Eve's physical bodies to be compatiable with the evolutionary progress happening outside the Garden.

"I want you guys to evolve, yunno? I made you imperfect, probably because I meant to, since I'm all-powerful and shit, but I changed my mind and I want you to be more optimal. Now, I could just snap My fingers and you could be perfect, instantly.

And, yunno, I totally would do that. But, even though you're basically infantile and know nothing, I gave you a temptation impossible to resist, and of course, you didn't resist. So fuck you, you assholes can suffer. I'm going to make you age and die and be capable of evil so I can be even more pissed off at your kid when he kills his little brother because I love his stupid offering more... not that this is going to make me step in and stop it from happening, fuck that.

I'm really not a fucking asshole, though, so you guys better love me if you know what's good for you."