The best answer I can find on why is Ajeet Gupta’s answer to Why do I have to log in to Quora to read content?
Ajeet Gupta argues that:
- Authenticated, eponymous users lead to higher quality answers—which is consistent with the Quora Real Names policy (which is severely undermined by anonymous users). But that does not explain why you have to log in just to read.
- Valuation: “Look! We have 10 million gajillion registered users! Please give us more money!” Which makes the most sense, though I’d have thought IP tracking has made tracking unique visits a solved problem.
- Establishing Token Cost (aka Keeping the Riff-Raff Out). Quora is invested in being better quality than Yahoo Answers, and if you can read, you can post—though it still seems an unnecessary extra step to force login just for passive consumption.
- Encouraging Community Effect. Having ID for who’s upvoting who is certainly useful to how Quora works (if only it weren’t in so much denial about being a social site); I guess they want the eponymous clicks badly enough, that they make you pass the extra hurdle of logging in: as soon as you can read the stuff, they figure, you’ll want to click and comment and answer.
There’s a cost in forcing login; I can only surmise that they think it’s worth it in terms of the increased quality of input they get, and aren’t worried about Reddit-like volumes. They get very highly ranked on Google, after all.