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Emojis mirror real life. In real life different people use different gestures to signal the same thought or feeling (e.g. one might fist pump in triumph, someone else might raise their hands Rocky-style, yet another one might stand there in the typical superhero pose). The inverse is also true: the same gesture might mean different things to different people or even the same person (the aforementioned superhero pose might also be taken as an angry parent berating their misbehaving child, depending on the facial expression). And lastly, a lot of gestures or sayings aren't globally used (e.g. "crossing your fingers" in English has an Emoji that doesn't make sense to us Germans who use "Daumen drücken" = squeezing your thumb as the corresponding saying, and there's no Emoji for that, so either we know the English equivalent and use that one ore we're simply out of luck).

As ambiguous real life is, you cannot make they pictograms trying to represent them unambiguous.

Same as any other piece of language, really, 'cause that's all Emojis are, a type of language we can use or not along the other types of language (spoken, written, body language, images, dance…). NONE of that is unambiguous. Of course the Unicode people know that; of course they don't expect Emojis to be universal.