They can't really push for advertising until they eliminate 3rd party API access to the content. That or they have to start charging a usage fee.
Which is interesting. One option they do have is to charge the user for using Reddit via an API, not the apps using the API. If you want to access Reddit via a 3rd party app then you'll have to pay for it - say something on the order of $1.99 per month or $19.99 for the year. I imagine they must have explored that option, so it makes me wonder why they abandoned it.