The principle issue I had with them was that they scale poorly. A few dozen principle feeds: OK. Hundreds or thousands, not so much.
You effectively see the same problem with Reddit forums, as a parallel. A smallish community of a few thousand subscribers, following the 90/10/1 rule meaning maybe 10 members submit 50% of the posts, another 100 contribute the other half is OK. A sub with 100k -- millions of members, both the submissions and comments are simply a firehose, and the temporal weighting (even with vote-based ranking) means arcane subjects slip off the page rapidly.
Algorithmic ranking => algorithmic gaming.
Temporal ranking => temporal gaming.
That is, the feed is dominated by the most-frequently-posting users.
Fixing this in a fair fashion for a large number of users with a high variability of interests is ... difficult.
In any large-audience medium, the default "show/no-show" decision for a piece of content approaches "no-show". Attention is finite.
(I'm not saying algorithmic social media is better. I'm saying the problem is hard.)
