Firstly, I’ll clarify stuff a little. I’m a teen myself, and if you ask me, we type in two ways that are like yin and yang to each other. One is all lowercase, abbreviating words (like “you” to “u”, “yeah” to “yea” or “really” to “rly”) and skipping apostrophes. The other is using more correct capitalization and punctuation, filling your text messages with metaphors and subjectivity adverbs and even using bolds and italics. And there’s barely an in-between between these two extremes.
Both happen because of aesthetic and psychological reasons.
Typing a whole text message of lowercase letters suggests kind of a laidback attitude, which is why a portion of people may choose this way of typing. Another reason is that, because there are no caps, the message itself feels more stable. Plus, people who type that way often think that using caps well feels too raw, so they prefer to take them out, strengthening the calmness they’d want to convey. Some others might do it because, in a way, it has become kind of a cult. And maybe that’s why that typing style is more expanded and stereotyped to Generation Z than the other. Obviously, no one would type that way in an essay or something more formal, but only in social media.
On the other hand, using an elaborated grammar and punctuation couldn’t feel as chill or laidback as an “all lowercase” message, but kind of the opposite. I think it feels more honest and expressive. Also more joyful and energetic. And that’s mainly why that other percentage of teenagers, myself included, prefer to type this way. And you’d ask me: If you always use a correct grammar and punctuation, how can I know you’re in your schoolwork or you’re just talking to your bestie? So if I want to be formal, I’ll speak more literally and go straight to the point, but when I’m speaking to my friends or my crush, I might be more metaphorical and use adverbs that suggest subjectivity, along a much more street-like language. And if I want to sound cute, I’d recur to repeating the last letter of a word/sentence (like when I say “Thankssss”). That combined with a more expressive way of explaining yourself is just adorable. And, just like in the first case, I wouldn’t fill an essay with metaphors, subjectivity adverbs, bolds and italics; that way of typing only rises in informal situations as well.
Anyways, I really hope you understand why our generation types in these two completely different ways.