I had the exact same realization after I posted if you see below (or click this https://news.ycombinator.com/item?id=44998664).

However, I wonder why it hasn't been done by text-based platforms like Reddit and Hacker News?

Reddit has the drop down with "New" items (for the "curators" to watch) and "Best" (presumably for once the items have been elevated to the front page). HN has the the same: the "New" link versus the home page.

Twitter is slightly different, and maybe more of what I'm thinking of, but the content is very different: short form, and original content rather than links to finds with an accompanying discussion. Similar, but not the same.

I wonder if that tells me that it just only works with "doomscroll" content — the kind of content where it's plentiful, short, and very little commitment to read each piece (and therefore very little time lost for a "poor" suggestion)? Or if there's something fundamentally different I'm missing?