Emojis are a means of conveying emotion in a succinct manner. Since certain emojis, such as the okay symbol, mean different things to different people, it loses it's effectiveness as a means of communication over a broader audience. https://en.wikipedia.org/wiki/OK_gesture
And emojis only work in response to written context. Try using only emojis to communicate a lunch meeting date, place, and time. You would need thousands of emojis to communicate effectively versus using a limited number of characters (26 if you're an english speaker).
Move along, nothing to see here!