I think many of us abandoned it when we went professional. Or abandoned it in those contexts but still do it in others. I don't do it on HN, clearly - but I do it almost everywhere else. It's much more natural to me to skip capitals.
I believe there was also a period in the transition to ubiquitous smartphones where it wasn't an option to turn off auto-caps, or maybe there just wasn't the fine-grained control of which auto-correct you use on mobile devices that there is now. I suspect that killed some all-lowercase habits. I think that's why I ended up with a "normal" style on HN where I use caps and normal punctuation (I don't usually use periods for sentences that terminate a paragraph outside of HN.)
However, for speed, I have recently abandoned capitalization and punctuation when interacting with LLMs, unless they are critical for clarity. I wonder if this is why many folks in the AI crowd write everything in lowercase.
For me it wasn't about being professional, it was just about learning to type. As my typing speed improved it just became second nature to capitalise where appropriate. In other words, I capitalise everywhere out of laziness.
I know I’m far from alone in having skipped your post entirely upon opening. Nothing personal, but I have yet to find a single post by anyone written in this style where the content was worth the effort of parsing non-existing capitalisation.
You go through the trouble of adding aids like syntax highlighting, lists, coloured titles, and even differentiated notes and timestamps. Presumably those are there to help the reader. But then you throw away a lot of readability by making everything lowercase.