Ancient glyphs and Chinese characters existed before Unicode, the committee didn't conjure a new form of language out of thin air. The decisions with Chinese writing were necessary due to practicality (there are various composable encodings, including IDC in the Unicode itself, but they're not very practical for a general-purpose text processing encoding).

Unicode emojis did not exist before Unicode, the existing composite emojis/kaomojis/etc were already perfectly expressible in existing symbols, and were nothing like Unicode emojis. This was a huge distraction from their mission, and definitely not inevitable.

Today's emotes became customized, and it's impossible to express them in any encoding. They diverged too much from writing to be called writing, it's a volatile signaling system at best. You can literally make an AI generation or upload your picture, how do you even encode or standardize that? But because of their blunder Unicode got stuck with its role of a judge and censor of a new entirely synthetic language it created, which wasn't the original purpose of the consortium.