Facebook's game is to show that they can act on the grand old online media promise: that they first get loads of users, then later they can turn on the revenue streams and the cash comes pouring in.
Facebook is living up to this promise with the way they turned on mobile ads and they are now bringing in over a billion dollars annually. I think they want to maximize on that opportunity first, then turn on another revenue stream after mobile ad growth starts to slow. If they pull this off, they will be Wall Street darlings
The only explanation I've seen that makes any sense to me, is that their ad systems are still immature. They haven't figured out how to properly monetize their own platforms fully just yet, much less the rest of the Web.
Which also helps to explain why they get rated so poorly on return-on-investment when it comes to ad spending.
I'd say the last year has been a substantial break-through for Facebook in terms of pushing their ad systems forward and getting wide adoption of it (including finally getting mobile to spit dollars). Maybe a couple more years of developing their advertising platform and they'll get there.
I also think there's a general underestimation of how good the Google ad system is overall, and how hard it is to compete with.
For Google, AdSense solved the problem of limited inventory, i.e. there were just that many searches for "digital camera" and AdSense provided an opportunity to boost the inventory of potential ad venues to people who don't actively search.
What value would a third-party ad placement program provide to Facebook, who's already sitting on trillion+ ad displays per day, and has no shortage of inventory?
Facebook is living up to this promise with the way they turned on mobile ads and they are now bringing in over a billion dollars annually. I think they want to maximize on that opportunity first, then turn on another revenue stream after mobile ad growth starts to slow. If they pull this off, they will be Wall Street darlings