A lot of Quora spammers will play the long game. Some of them will take the time to get moderately familiar with a subject, write some organic answers, gain some karma on the site, then start shilling. It's an interesting incentive structure, but ultimately most answers on the site end up being the mediocre filler by spammers trying to build their accounts.
Somehow or another, Stack Overflow is able to maintain very high quality threads. I'm not sure if that is because of filtering algorithms, or human moderation (which is more or less crowdsourced).
I have not run into this kind of spam on SO.
There are a lot of "Kool Aid" threads, where folks get heavily invested in a technique or pattern, but those are legit, if somewhat tiresome.
And before someone says 'Stack Exhange is just as broad as Quora' -- all the SE sites I've come across disallow 'product recommendation' questions or whatever similar thing fits their niche.
SO has human moderators and a points system to gate functionality, and those points are earned by being useful.
Quora did have a points/credits system in the beginning but they removed it for some reason, and ever since then participation and edits were open to everyone which let the spam take over. They also have a faceless AI-powered moderation system that's often overbearing and wrong.
