Some people use Facebook as a primary means of keeping in touch with family.
Some people's Facebook networks mirror their family-and-friends networks.
It's socially awkward to unfollow your relatives, even if you don't particularly want to see what they post, or can't deal with the volume they post.
But it's not socially awkward for Facebook to notice what you do and don't engage with, and try to show you more of what you engage with, regardless of who you follow.
If you treat following someone on X, or Fediverse, or Bluesky, as nothing more or less than a means of seeing what they post, then you can carefully and selectively choose who you follow, such that your chronological timeline is a manageable amount of content. You can choose, for instance, to not follow people who post a massive amount of content, or whose content you mostly don't want to see. You can make lists for people whose posts you might want to sample from time to time and not read all of. You can rely on other people you do follow to repost things that are interesting.
But if you're following so many people, or such high-volume people, that your chronological timeline is a firehose you can't possibly read all of, then an algorithmic timeline becomes more tempting.