I'd love to hear more about why. It makes sense for YC (and is probably being treated as a normal investment rather than "Adam filled out a YC application and did a 10 minute interview"), however I feel like it makes Quora seem weak.
I'm hopeful Quora will too--as the YC community grows larger, we can help companies in lots of ways, including with things like hiring that are particularly important for later stage companies.
So starting with awesome people creating awesome content helped. Over time, Quora has done a few things really well: (1) growing the community while keeping it fairly high brow, (2) their topic taxonomy, and (3) their email digests.
My problem with Quora is that it's more entertainment than useful. SE/SO is more functional. Who really cares what are the things about San Diego that most people don't know?
Seems like there could be some potentially misaligned incentives for YC founders there...
YC seems ideal for this. Just because they've spent millions, doesn't mean they aren't stuck, and need that magic juju sauce help to do the perfect pivot, which YC can perhaps help with.