Most successful social networks and internet platforms generally have relied relatively little on advertising for their growth. It is sometimes used, but only sparingly as a narrowly targeted boost to an existing growth engine. Without being able to organically grow through word of mouth, as well as retain users who do join, advertising can just turn into a huge money pit.
If we are able to crack the growth engine challenge and show that a particular form of advertising has a sustainable positive return, then funding for it can be proposed through the SPS (part of this hardfork).
RE: Open Letter to all Steemians - Hardfork 21: Culture Change