So I looked it up and as I thought, the core basis of sorting for reddit is based on a weighting algorithm looking at thumbs/comments. People suspect that other information, like locality are used to (hence you typically get posts in your language), but there is supposedly limited user based info used in the ranking of posts (people generally see the same content on r/all)

What I was hypothesising is that reddit wants to get rid of r/all so they can create a more tiktok/Instagram like feed based on individual user behavior. Both to make the app more addicting and/or have greater control/influence on what you do/don't see.