We moved on from hieroglyphs since writing by hand was so tedious anyone bothering could be assumed to be serious in unclear cases. Since writing and sending messages has moved on to an everyday form of personal communication, it also requires a concise way to express tone and emotion a non-professional writer can manage.
Excuse me if the following sounds a bit exasperated, but you do realize that people actually communicated informal messages to each other written form BEFORE texting, right?
You went off the rails there. The earliest writing was only used professionally - there just wasn't any vocabulary (at least none surviving) for anything but accounting. Using writing for sending messages from place to place was an evolution, and not an instant one. The earliest messages seem to be accounting/business related as well, from tax information to contracts to customer complaints. Since you had to send a human messenger anyway, who was perfectly capable of memorizing long and detailed messages, sending a written message with him was a somewhat specialized need.
It was only with the growth of the idea of using writing to send a message through time, and/or in multiple copies throughout the land, did written language become expressive enough to be useful for "informal messages" in a way that the person carrying the message wasn't. Laws, histories, treaties, and so one required more vocabulary than common trade objects, numbers, and "promise to pay".
Even if we include common and nearly universal body language gestures like nodding, shaking the head,
There's a girl in my office new enough to the US that she still shakes her head from side to side as an affirmative gesture, which is common for at least a billion people. Everything's arbitrary.
By the way, the one emotion/tone that has frustrated writers for centuries is irony/sarcasm. Many have proposed a simple symbol for this, usually a backwards question mark. But for some reason no such mark has become standard. That's perhaps the only "emoji" I have ever felt the need for in writing.
I find it interesting that this is also indicated by tone of voice, well within the normal sort of thing modern language captures. We use punctuation and accents in many ways in many languages to capture tone of voice. Isn't it odd we don't already have something for sarcasm?