I think Conde Nast bought Reddit thinking they'd be able to turn it into Disqus, which didn't exist at the time. Then their network guys got a look under the hood and determined that while they could implement it, they'd need to rewrite it, hobble it, unfuck it and otherwise gut it in order to turn it into a well-heeled hierarchical comments system. So they let it run for a while to see what happened with it - after all, it was a sunk cost and it didn't hit their bottom line much. And besides, they got to look edgy and forward-looking in a way that Wired accomplished back when Douglas Coupland was still cool. And since then, it's been prominent and interesting and they can't offload it without it looking like a failure... but I think it's a pain in their ass more often than not. Twitter went public before people figured out that it has essentially zero value. Reddit did not. Dumbass A16Z poured what? $40m into Imgur before they figured out that it needed to become photobucket to make money? It's always been weird to me that the valuelessness of 4chan is immediately obvious to everyone but people think Reddit hasn't made money yet because they haven't cracked banner advertising or some shit.
When people who don't understand computers are told that something on the computer is important, they believe it. Pets.com raised $82m despite the fact that Petco and Petsmart were closing stores and consolidating. Twitter is top-heavy because journalists use it and it's easy to embed within online news therefore it must be important, right? And if it's important, it must be worth something? And if it's worth something, surely we can trade for it? The thing that reworked my understanding of finance was greater fool theory.