The medium has much to do with it. When I was in middle school, we didn't have cell phones. As a result, we would pass physical notes about between classes. Those notes often included a lot of pictures, capitalization, underlining, etc; I don't think that this kind of ungrammatical parlance would have translated well on physical paper. There's something about the act of typing that makes it effective. I'm using voice to text more and more, and I'm starting to see some evolution in my communications there.
I recently read this. I think a few of these apply to this article, particularly #1: Anyway, what I think we're seeing is actually the reshaping of the informal register, or perhaps even the emergence of another informal register. Textual representation is certainly a way to play with how the language and its gravity is perceived.1. Confusing grammar with spelling, punctuation, and usage. Many people who write about grammar seem to think that grammar means “any sort of rule of language, especially writing”. But strictly speaking, grammar refers to the structural rules of language, namely morphology (basically the way words are formed from roots and affixes), phonology (the system of sounds in a language), and syntax (the way phrases and clauses are formed from words). Most complaints about grammar are really about punctuation, spelling (such as problems with you’re/your and other homophone confusion) or usage (which is often about semantics). This post, for instance, spends two of its twelve points on commas and a third on quotation marks.