Social media platforms were always badly positioned - they are failing by design. They have been able to grow in order to outrun their problems, but this cannot be sustainable because the flaw is fundamental.

I think the idea is effectively conveyed in the intro:

In the game of Go, bad shape is the term for configurations of stones on the game board that are inefficient in achieving their offensive goal (territory capture) and unlikely to achieve their defensive goal (the state of "life"). You can extend a bad shape in a fruitless attempt to make it better, but you'll generally be wasting your time.

The idea I keep coming back to is that the big platforms, like Marley, were dead to begin with, and are now something particularly bad, which is dead on their feet. Not because they’re been abandoned by users (yet) but because they’re structurally incapable of governing the systems they made, and most of the things they try to do about it introduce more and weirder problems.