You see it start to change with the telegraph on down to where we are today.
Telegrams were paid by the word, and were all uppercase by design, they're not an evolution of language. It took more effort to adapt your message to a telegram than to write a proper sentence.
I wouldn't spend nearly as much effort on something ephemeral and instant. For instance, I'm not going to mail my sister in another state a letter saying "ok thanks". I very while might text her that, because 1) she knows exactly what I'm referring to — the thing we were talking about 11 seconds earlier; 2) the customs of messaging mean she doesn't expect or want a wall of text; and 3) if she has any more questions, she can ask them and I'll reply within a minute or two.
The modern devolution of spelling is just not giving a fuck about norms and courtesy.
"Dictated but not read."