There is a LOT standing in the way of monetization for Reddit:
- younger user base (so less disposable income)
- loose concept of user identity, so can't tailor ads
- more corpoarate and mainstream advertisers tend to stay away due to the nature of the community and content shared
- primary usage is on web rather than mobile apps
All of these are fixable, but the question is can they do so without alienating their use base.