Because it's by far the dominant strategy for distributed trust-ranking systems out there, with decades of research around it. Might as well look at the forest when realizing that it'd be nice if trees existed.
And I don't think anyone actually trusts any major actor to verify anything, so a fully centralized system is likely out. Otherwise people would be hype about WorldCoin, instead of recognizing it for the stupendously malicious grift that it is.
Why are they doing that (i.e. being sarcastic)? Who knows.