One of the principles of Unicode is 1:1 round-trip-encoding to every other encoding, which is why there's so many pre-composed letters and accents even though t

One of the principles of Unicode is 1:1 round-trip-encoding to every other encoding, which is why there's so many pre-composed letters and accents even though the individual letters and accents are available separately. All the encoded emoji have been used for decades by Japanese phones; it's certainly not as well-thought-out as the rest of Unicode, but Apple and Google needed to have some common representation of those characters in their Unicode-based software so they could interoperate with Japanese telecommunications infrastructure. Adding emoji to Unicode was the least terrible option.