(1) Most platforms (FB, IG, Twitter, TikTok, YouTube, Netflix) rank content by predicted engagement: they'll show you the items most likely to cause you to click, reply, retweet, etc.
(2) Ranking by engagement increases retention. Users shown ranked feeds spend more time and return more often (higher DAU), compared to users shown unranked feeds. Platforms care about retention above all and thus they maximize engagement primarily as a means to that end.
(3) Ranking by engagement hurts quality. The most-engaging content often has high shares of clickbait, spam, scams, and misleading headlines. Low-quality content tends to hurt retention and so platforms are constantly trying to weed out engaging but low-quality content.
(4) Ranking by engagement increases "sensitive" content. It shows more nudity, bad language, abuse, hate speech, & partisan politics. In many cases decreasing sensitive content has a neutral or negative effect on user retention, so platforms are unsure what to do about it.
(5) Platforms would prefer to have less sensitive content (for a variety of reasons) but they also don't wish to be seen to be making value judgments. As a consequence they often are slow to intervene, both on quality and sensitivity, and they intervene in roundabout ways.
(6) Incorporating explicit user preference typically doesn't make a big effect on sensitive content. E.g. if you ask users survey questions they often seem to like the sensitive content.