We, as programmers, would basically have to start from scratch. And we need many people to have a "wall server" before we could get the reluctant people to sign on.
There is not a good way to onboard all the people. With F-c-book, you just make an account and start using it. There wouldn't be that satisfaction for most people. You need your friends on it first. So....
Anyway, if you actually watch what F-c-book made. The sucked people in, and then took over their feed. And they really manage your dopamine levels and your happiness. The adverts are just their as camouflage.
Building something people join together often matters more than the technology behind it.