There's also the "we can only pay a third of what Google paid you..." and given two candidates that interview equally well, one is former Google and appeared to be making $300k and another is from somewhere where they were making $70k before...
I'd argue for the $70k person. They are less likely to have experienced lifestyle inflation and looking at this position as a "slumming it until they can get a job making $300k+ again."
It further complicates the issue that most companies don't have Google scale problems and don't have the engineering culture for a Google scale solution.
There are several factors working against even not incompetent former Google employees - especially if their experience is entirely within Big Tech.
A bit ago a former Tesla person was in the set of interviews and it became clear that they wanted to make the organization that was considering hiring them into a copy of how Tesla works... and that wasn't something that was going to be doable. The post interview discussion was "this person is going to try to make us into a copy of Tesla for six months, and then leave shortly after they realize that we weren't a place that could become another Tesla."
Big Tech experience may be a positive signal for getting hired at other Big Tech companies... but it can be a negative signal at a company that isn't trying hiring for an organization that can't become a Big Tech company - especially if that is the only thing that is known.
Hiring isn't necessarily picking the "best" person for the role, but rather the least risky. Former Big Tech employees are often riskier than other candidates given their lifestyle expectations and the mismatch of the engineering cultures.