College-only Facebook would have died after everyone graduated and it really took off after they decided to compete with Twitter's feed. The model of having a stream of news of people complaining about what they had for breakfast allowed grandparents to get massive FOMO and join to see what their grand kids were up to.
Zuckerberg for all his flaws has always had an eye for what the next big social media wave is and went after it.
Agreed, but I think a(n unintended) side effect of college-only was to drive the demand.
Things we utterly hated, like turning a pull-only format of "let me view my friend's profile" (which later became "what's changed is in yellow") into the push style "newsfeed", and requiring real names, really made it what it is today. Obviously there are still fake accounts, and people aren't all using their real names anymore, but it's so much closer to a "real" profile than anything else out there.
But yeah, especially the newsfeed. Making users poll friends' profiles never would have resulted in the engagement they require. Frankly, the platform would have died because user interest/engagement would have gone elsewhere.
Zuckerberg for all his flaws has always had an eye for what the next big social media wave is and went after it.