[tyingq]

Just a guess, but I think when they started losing the spam wars they put in some kind of handcrafted whitelist ranking boost, either directly based on brand/site, or link proximity to known good sites, etc. And maybe they don't update that list too often. You can find some info about an ML update Google called "Vince" that sounds a lot like that.

[MichaelZuo]

Not updated in over 2 years?

[tyingq]

Not updated in a way that affects Quora over many years would not surprise me.

[MichaelZuo]

How could that even work to not affect one of the most popular sites whatsoever?

[tyingq]

Poor maintenance of a probably thousands long whitelist of "brand quality" seed sites? When the only measure they really care about is ad revenue, and bad organic results might mean more ad clicks? It's not really that outlandish, just plain complacency from a company with an overwhelming market share lead in search. That's how Google started in the first place...capitalizing on complacency/stagnation on the then leaders in search.