https://support.google.com/webmasters/answer/35769?hl=en
Quora presents a very different site to Google than it does to the reader ultimately. Google intentionally, knowingly ignores this fact and has for years. They could manually penalize Quora for breaking Google's search quality guidelines in numerous ways and they choose not to.
A user can't freely browse Quora page to page, whereas Google can. Presenting a different site to Google than you do to the user, is about as direct of a violation of their guidelines as you can get.