I disagree. The issue is not exposure to customers, it is the mindset of customers. The market has matured as smartphones have become ubiquitous and free apps have come to dominate the market. Direct sales have simply faded because they are less lucrative at the highest level, and users have re-based their perceptions around that. Even if you could get your paid app to the top of the charts and attain maximum exposure, you would still make less than if you had used a fremium or ad-based model. Why do you think all the highest-grossing apps are free?

I don't think this is a particularly surprising phenomenon. People work very hard for their money and have far too little of it. If they can get something for free, why would they not? Moreover, if everyone else is distributing their thing for free, why on earth would people pay for anything?

Money is valuable because it is scarce, and if people can avoid paying, they will.