I disabled my Quora account when I discovered it was selling my data.

I got rid of mine when they started paying people to ask questions, and the quality of questions plummeted. Also, the clearly fake "so-and-so would like you to answer a question" email notifications annoyed me.

SEOs happened

This community happened to it. The number of top-voted hacker news blog posts talking about how they acquired their first n users by shitposting on Quora about their startup are too many to enumerate. I think the difference between here and Quora is that the mods here are more opinionated and will kill posts that feel spammy/use voter rings/etc.

External links from Quora have the rel=nofollow attribute, so they don't help with SEO. Most SEOs would understand this.