Something that the "write for yourself" crowd either isn't aware of or deliberately ignores is that writing doesn't inherently come with sharing. Authors could easily take them at their word and write for themselves, and leave their fics on their harddrive/in their notenook/wherever they write because it doesn't need to be on a public site for the creators themselves to have access to it. But then the rest of the fandom would cry bloody murder over being deprived of their entertainment because what they actually mean when they say "write for yourself" isn't "write for your personal enjoyment" it's "do the work (that I benefit from) and don't complain."
I'll tell you and everyone else a little story. I didn't post all that much last year, but I actually wrote quite a lot but 95% of it either happened in discords where I wrote for the people there, or sits in my fandom folders. They're in a perfectly fine condition for me, but they need some polishing to be released into the wider world - for one thing I'm ESL so the grammar needs an overhaul for a start - and I'll be honest with you all, I don't really feel like doing it most of the time. It's a whole lot of work for largely no return at all.
Because you're so absolutely right. "Write for yourself" never meant "write for your own enjoyment" because once the writing is done there's a whole lot of editing happening before that is fit to be posted, at least for most of us. And that job? That's never something we do just for us, it's tedious, annoying, and very time consuming.
And I'm seeing more and more writers feel like I do and post less or just stop, and I know of more than one new writer who don't feel like posting their things in public at all because they know they won't get any response. So their writing is also in private and it's an open question if any of them will ever post anything publicly. Even before I saw the numbers on that post with almost 75% of fic on AO3 having 5 or fewer reader comments I knew numbers was bad and couldn't in good conscience tell them that things would be fine.
Now that I have seen them I'll be honest with you all. I think fandom is on a self-destruct course. It simply isn't a sustainable system to expect writers to keep posting things when the overwhelming probability is that it will get 0 attention.
As someone put it in the comments of that post, fan works - fic, art, gifs, ect - are gifts, gifts we give to fandom. But for how long are people willing to keep giving gifts when the ones receiving them can't be bothered to spend even two seconds saying thank you? It's a battle fo attrition, and until fandom gets its head out of its ass and loses the mindset of "we don't owe authors anything!" then it cannot be reversed. The question is if fandom is willing to lose that mindset before the battle is completely lost.