In that case, i could imagine for example that this can be something done to ease a further AI feature. it is almost impossible to train an AI for content with individual customization. So if Y is blocked to see your content, that is impossible to have AI trained on your tweets and still be sure that Y can't get the content of your tweets.
It's his site, they would code up whatever he asked, X is no longer design by committee. Remember when the Reddit CEO/owner/whatever was hand editing the database to alter users' comments to make it look like they posted something they hadn't?
Maybe they want to keep the code simple or ready for immediate open sourcing if desired.
What kind of decisions? Why?
The motivation seems simple: increase engagement by broadening the amount of content someone can see / be shown.
You will see what will come next and it will be clear.
If not for AI indexation, another hypothesis is something like removing the paywall needing an account to access user content or something like that.
Engagement scales with outrage. If there is a singular marker of outrage, it's in blocking.
> not for AI indexation
Why would Twitter want to help third parties train their AI on its data? Musk already has an AI venture. If there were a secret agenda around AI, it would be in reducing visibility. Not increasing it.
> removing the paywall needing an account to access user content
What paywall? The sign-in wall? Again, why would Twitter have a hidden agenda to undermine something Twitter is doing to boost user numbers?
These hypotheses are incoherent because they don't stem from any observations, but are trying to work backwards to justify the existence of a hidden agenda.
Regarding the other hypothesis related to the "sign in" wall, based on number it looks like that this wall is not working anymore to boost users as the number of users is collapsing. So there might be a plan to enlarge "page views" and so user engagement by reopening the Public view of tweets.