Reddit is an incredibly valuable service. Maybe a lot of people on Hacker News don't see this, but reddit has basically become the Geocities of online discussion communities. The subreddit system has eliminated the "eternal september" problem, since all non-casual users will trickle into the communities that match their interests. Even if reddit loses 90% of its users, it will still be a highly relevant online community. I am certain that they can turn a (modest) profit if they really try.
Reddit will probably never become a massive money machine. But regardless, it is a very influential community. Even community is arguably an understatement at this point, it is really closer to infrastructure. As I have said here before, I would be willing to bet that it is still around in 10 years, with a significant (millions) amount of users.
I can - sort of - confirm they are not trying hard. Last time I tried to advertise on Reddit, I failed because they could not accept CC payments from mainland Europe ... Just think of all the ad revenue they are losing.
If you advertise on Reddit, you're advertising to a violently anti-corporate anti-advertising audience, who may love you, but very well may hate you. You could be subject to a witch hunt at the drop of a hat.
I very much doubt advertisers would be lining up to advertise to that crowd. They're hardly big spenders either.