Quora just raised money at a billion dollar valuation basically. By comparison, Answers.com, a much larger site by traffic (with a $7+ cpm rate), was purchased for a mere $127 million, and was struggling to punch above $20 million in annual revenue.

Then you have to ask: what about Quora being worth $3+ billion, so their investors can get a return? There's no scenario that will ever get them there in the Q&A space (it'd require ~$300 million in revenue, literally impossible for them to pull off as is). They have to pivot out of Q&A because they can never justify their valuation, and they know it. To be worth that much they need to be a top 50 site in terms of traffic, and they're nowhere near that.

Wikia for example is substantially larger than Quora, and they couldn't even get close to justifying a multi-billion dollar valuation via advertising. Or consider Angie's List, worth $700 million, but tracking toward $300 million in revenue. Quora's investors have a huge problem ahead of them.