The "labor supply" side isn't the only factor in downward pressure on the value of apps--it's also the quality of the demand side. People tend to the cheap side when it comes to paying for apps. The result is that each marginal increment of "value" in an app comes with a geometric increase in cost to produce it. It's also a feedback loop: people aren't willing to pay (very much) even for good apps because there are a sufficient number of developers doing it "just good enough" and giving it away for free, and so developers who could make an even better app shy away from doing so since the prospective benefit doesn't merit the risk.