It is a very good question. While I am not in the thick of things as far a management is concerned, but as a stakeholder in the steem blockchain, there are some reasons why I feel such an ambitious project has been ignored or delayed so far.
First is that steem is still in Beta mode, and as such still very much an experiment. Being the first of its kind, it has sought to address challenges that arise to inhibit the success of such an ambitious project. As developers and the community try to forge the best possible pathway for the platform, having such a large campaign may not be feasible/beneficial to the platform at this stage.
Furthermore, the cost of advertising on such a scale is one to consider and usually runs into tens to hundreds of millions - one which we simply cannot afford at this stage (in my opinion).
Steem has also been restricted by the mainstream 'assault' on cryptocurrency adverts that saw platforms such as facebook, Twitter amongst others place severe restrictions on advertising.
The vision and decentralized nature of the platform also ensures that responsibility does not lie with Steemit.Inc for adverts/growth alone. Perhaps with the coming of Smart Media Tokens, we will see community led pushes from the various communities
I think we will see more community led advertising campaigns (like we saw with the Netcoins listing) in time, especially as the platform grows. If/When it reaches a relatively mature stage of its growth (like with the success of Smart Media Tokens), then we will see a lot more funded campaigns.