People will say they only want content from friends, just as they say they want to eat healthily. But the desire and the reality end up looking very different.
People at large will spend time in whatever surfaces are the most engaging (~addictive), and if a platform like Facebook removed those "other posts", it's likely that people would just spend time on another platform instead -- TikTok, Reddit, YouTube Shorts, etc...
It's like if the #1 grocery chain removed all the addictive stuff. No junk food, no soda, no alcohol. In the short term, people might consume less bad stuff. But in the long run, the #2 chain would take over, and we'd be back where we started.
I'm not saying this is a good thing, but it's a very tricky problem to tackle at scale.