I couldn't agree more; it's hard to attract people from outside the community, but think it's not impossible. The thing is that because they are not part of the community, and thus can't vote or comment, it's hard to keep track of how many people you actually reach with external promotion.
I think SteemIt should be implementing a traffic analytics feature.
Since you have a degree in marketing, don't you think it's frustrating how limited the options are when it comes to reaching a broader audience?