They could've easily expanded into more social features, longer-form stuff like Livejournal, personal creative stuff like Deviantart, and personal creative/selling like Etsy and Bandcamp and print-on-demand books, etc.
Another killer feature they flopped on was personas. Nobody really wants their entire extended family, current former and potential coworkers and bosses, customers, preacher, old friends, romantic interests, drug dealer, and fetish group all hanging out together in the same room talking. So people made separate accounts and different names but Facebook continually fought hard against that very basic nature of human social networking.
Instead of any social-networking improvements to their core, they just removed all the value from the feed. And then bought out another messenger and another place to post photos, both of which they already had. Then a halfhearted videos thing and now a VR Second Life clone.
Facebook needed to fill that gap with content from elsewhere. That's where influencers and content creators came in. Who are way less interesting than your friends, but they do post content regularly.
I don't think facebook had a choice.
It's like only one in ten SMS texts would actually reach the other party: people would complain about SMS being broken just like they complain Facebook doesn't show them what they want to see.
Instead of your friend's posts you will see half a dozen random posts from your friends each day, too often from one prolific poster, and the rest is ads or group spam. Why bother writing anything relevant, deep, or fun when only a fraction of your friends will ever see it.
I think that Facebook's only real revenue option that would have also retained the fundamental value of the social network and its effects was to behave either as a third-party sentiment/preference analysis service ala Nielsen Ratings or as a source of ad targeting for individuals (based on their sentiments/preferences expressed within FB) that could be sold for use external to the FB experience... and I have suspicions that even the latter might have eventually led to distorting that core FB experience.
The social network and the behaviors within it were only truly valuable if externally observed without intervention. By pushing behaviors that FB itself wanted users to perform they broke the uniquely valuable part.
There used to be way to view posts off a friend list, and you could then create a list of all of your friends to emulate the old newsfeed (or The Wall). This at least tried to work except it also only tracked back so far, it still did miss posts (but not as many as the other two views), and most importantly the friend list feed was scrapped last year.
I hope they hadn't even tried. Initially, Facebook offered lots of value in the early years in the form that users were actually able to follow their friends' lives and stay connected. You had a bunch of friends and you would see a mostly chronological list of what they had posted that you read until you recognized something you had already seen. If they had kept it that simple Facebook might actually be something I'd be willing to pay for. The newsfeed is absolutely the core of the product and they started ruining it about ten years ago, and very steadily at that.