Before the app store model became popular, it was much more expensive and difficult to get your content published. Until 10 or so years ago, the most common channel for selling video games was retail, which meant you had to go through a publisher who -- if you could convince them to publish your software -- would take a massive chunk of the profits.

It's no mistake that the "golden age" of indie gaming has coincided with the availability of platforms like Steam and the mobile app stores. 30% might seem like a lot, but for many developers, it's probably much less than what the channel is worth.