One reason to pick emoji is visual distinctiveness and user familiarity. While admittedly there are large populations familiar with CJK ideographs and their con

One reason to pick emoji is visual distinctiveness and user familiarity. While admittedly there are large populations familiar with CJK ideographs and their construction/deconstruction, there are many more people familiar with emoji at this point. In the case of an encoding error or trying to visually "diff" two encodings, many audiences will spot emoji differences and/or problems with badly encoded emoji (much easier than they might spot differences in CJK ideographs). (Admittedly there are still issues within the emoji space such as some of the "faces" are quite similar in appearance in many fonts and still easily confused. Plus in the larger emoji space the subtle differences of skin color/gender can be easily confused if you have to rely on them for distinction. Restricting to only 1024 emoji and fewer ZWJ sequence variations presumably takes care of most of those issues.)