I think you're on to something with the marketing issue. There could be a negative feedback loop where:
Subject X is not advertised to Group Y because they aren't perceived as interested -> Group Y don't see advertisements and are therefore Subject X doesn't capture their attention so they are less interested -> Subject X is not advertised to Group Y...
With the ability of modern targeted advertising to focus on certain groups by age, gender and more, this really could become (and likely already is) a problem. I'm hopeful that the free market will balance by making it more lucrative to take the risk of advertising to groups of people that seem less interested by balancing with the reward of bringing in all the untapped potential users.