> Why are we criticizing Facebook's models that we basically played our own individual role in building?

Practicality and precedent. We can effectively regulate the algorithms a countable number of companies use in their products, but can't effectively make people not susceptible to doom-scrolling (nicotine, heroin, gambling, whatever).

> If Facebook went away tomorrow, another platform would fill its place.

Not if the troubling practices were illegal or too expensive to operate. It would be a pretty dumb investment to bother. Instead, new platforms would pursue different techniques for content presentation and profitability, just like existing competitors already do.