A "free" ad-driven social networking site that brings in gigantic revenue, but that has to pay thousands of high-priced engineers to implement all of the cruft you just described.
versus ...
A subscription-based, non-ad-driven social networking site (perhaps operating as a member-owned cooperative?) that brings in much more modest revenue but that also can operate with many fewer engineers because it can be largely cruft-free.
I know there have been a gazillion attempts at the latter and none has succeeded in any way comparable to the "free" sites. It's too bad, because if any of them were to ever achieve Facebook scale, the subscription price would probably be quite modest.