> Unicode needed to include written-on-paper glyphs that existed in the world.
If it was the case, Emoji is seriously lacking a penis. I mean, seriously, give men a way to draw and this is what you will get. There are already existing "subjective combinations" like 8===D and the eggplant emoji for which it is its most common use. There is a proper penis in the hieroglyphics, but just because there is a hieroglyphic doesn't mean there is no corresponding emoji (ex: eye).
On the other hand, many emoji pass even though I have never seen anything remotely similar being scribbled ever, it is the addition to the emoji block that drove its use. Plus, because inclusivity, all its equivalents in different genders, skin tones, cultures, etc...
Clearly, Unicode acts as an arbiter here. It decides on what it thinks it is "good" rather than what is really in use. And it is not just about penises, the hangman is also absent, as is the "gun pointed on head" sign (suggesting suicide) that is commonly used in real life.
Worth noting that the first emoji were included because they were already in common use before Unicode, in Japanese phones specifically. Unicode just included them so that Japanese users could switch to Unicode without loss of functionality.