There's more to it than just rendering images. As you mentioned, there's coding, but there's also good writing and story-telling as well as planning out how various actions lead to certain branches and how that will play out down the road etc... etc... etc... the story (or as devs often word it "script writing") takes about as long as the rendering due to the complex branches the story can have.
I can render just fine, with inferior hardware at that, but coming up with a good story is very difficult for me. I don't know about others, but I like a really good story more than anything pornographic.