I've unfollowed friends. I don't unfriend because I do like them, and want to stay in touch, and I'll still check their page and comment/like when appropriate and send messages.
I've only unfollowed 2 people. Both were because they were completely taking over my newsfeed. They posted so many times a day, and shared, liked etc etc so much content that I saw practically nothing else in my newsfeed. And the things that were popping up did not at all interest me - for example one of them posted a lot of vintage pin up girl posters and vintage comic book content. It started to get vaguely offensive. So I unfollowed him. We're different people, with different tastes, and that's fine. He's hilarious, and I genuinely like him, but his facebook style is not to my taste so it was better all round to just unfollow. There's a lot more to him than what appears on facebook and I didn't want facebook tainting our friendship.
That said, even though I've only unfollowed two, facebook certainly doesn't show all my friends in my newsfeed. I think they have algorithms that dictates who pops up the most. So just because certain people don't seem to interact much it doesn't mean they've unfollowed you - facebook might not be showing them your content for other reasons.