Example: Everyone who even knows someone who makes $500K at Facebook seems to love posting about it here, but nobody who makes $100K there seems to feel the need to boast about it.
There are tons of low level employees posting their salaries. If you work in those roles, that data could be more valuable to a candidate than Glassdoor's amorphous projections.
I think the user behavior that facilitates this is the same behavior you see represented on Blind.
https://www.levels.fyi/offerings/
They also have users upload W2s, offer letters, and supporting documents in addition to proof of identity.
https://www.levels.fyi/verified/
They have their own job advertisement business and they partner with third party recruiting companies to get anonymous data about offers candidates receive.
They also just take having accurate compensation information seriously so they do things like outlier and forgery detection as well as seeming to have a much better algorithm for processing the information they receive.
It's possible, but I know that salary information isn't at all what I'm interested in learning from such sites.
And based on my attempted use of the site, Glassdoor is unreliable and (intentionally) misleading.
Even at the most basic level, their UI flatly lies about what data they possess. If you search a company, in the salary column it will show a number which is designed to suggest a number of salary data elements available. Honestly I cannot say what that number actually means as it seems to have no value at all. Specifically, it will say 5 or 8 or some other small but non-zero number... and yet there are zero visible salary records for the company (even if you are a contributor of information and thus deemed to be allowed to view other information on the site).
I expect Glassdoor is like the many dating sites on the internet - full of fluff and false/artificial information so the site appears to be valuable and worth visits.
If we ever reach a point where company position salaries are public on a broad scale, Glassdoor will fade into obscurity.