Seems that's the major flaw in self-reported salary aggregation sites: Because it's self-reported, you're generally going to get only one side of the bell curve: The side that people feel good about reporting. The FAANG employees, probably just the subset of them that are well paid. Who wants to go to a web site to report to the world about their utterly modest, average salary? How depressing! I wouldn't want to.

When I go to a site like levels.fyi looking to compare my comp, I'd have to believe that I'm not seeing "average" engineering salaries, but an average of the very best salaries at the very best companies. EDIT: Looks like you addressed my question in your comment already. Removing it!