But if we try, we can rise above nature. We can separate from the system and elevate ourselves above it. In short, we can become kadosh, holy.
We can thereby become, so to say, like Hashem - the Creator - Who fashioned nature and rises above it. קְדשִׁים תִּהְיוּ כִּי קָדוֹשׁ אֲנִי , Be holy because I am Holy.
That is why kedushah in particular is associated with arayos.
Many forms of stimuli excite us and hold a powerful sway over our nefesh habehamis. The pizza in the example above could be exhibit A, and in fact kedushah is mentioned with respect to the consumption of forbidden foods.
But perhaps the most powerful of these stimuli is the desire for arayos. It draws us in and appeals to our base instincts so strongly that it can render us nothing more than animals. Think about it. Those selling ervah and those buying it clearly relate to themselves as nothing more than beheimos.
Therefore, although kedushah is mentioned in the Torah with regard to many mitzvos, it is most closely related to abstention from arayos, as Rashi states: “Be holy - separate yourself from arayos.”
To rise above it all, to separate oneself, to choose, is to achieve kedushah.