You need a source of trust in these systems. Journals used to have that role. They had high standards that were upheld by editors selecting only worthy publications. Today it seems that many journals aren't as trustworthy as they seemed to be in the past. It's also easier to spam the journals with your publication and to bullshit your way into publication. The incentives to publish a lot are also way higher now that your grant money is highly dependent on your citation count. Journals can publish more and easier and lower the standards for submission to earn more money. The system is basically eating itself and we haven't found a cure yet.

Filtering for self-citations is useful to identify the bubbles. But it is not sufficient to determine if those bubbles only contain hot air or if these scientists are actually working on something with substance in a narrow field where few others publish.