That just redirects the lust. Making it morally wrong to do, doesn’t stop the biology. If your hard-coded to try to eat an apple every time you see one, unless you really, really hate apples, what’s stopping you from shutting down that process?

That’s the human take on sex. The only difference is; instead of “you disliking apples”, it’s “everyone understands incest is wrong”, so that’s why it doesn’t happen (or, is starting to happen less). I believe the prevalence of “step-sibling” porn is proof that there’s still that primal desire, it’s just being masked as a more “politically correct” and “modernized” experience.