I think the reason for the distribution is just due to the terrible discovery on the Appstore/Google Play. It's completely hopeless to rely on users stumbling across your app on the store, and the only real way to get users is by advertising/paid user acquisition. The problem with that of course is that you need significant funding to run a successful ad campaign, and "the little guy" is not likely to have that funding nor the knowledge/experience.

And of course just like websites have learned how to game the Google search algorithm, they can do the same for the app stores, which the top publishers certainly have done.