Since the beginning, one of the top ways that people discovered new apps for iPhone, iPad, and macOS has been through the Affiliate Program. Through the program, websites and influencers alike could promote one or more apps and make a small commission on sales. The program is what has made app review websites possible, which makes finding new apps easier while giving a consistent view of these new apps.
The program was responsible for 7% of all app purchases in the store in 2017 - a huge symbol of success. The success of the Affiliate Program has been in large part because of the overall lack of discoverability in the App Stores themselves. Over the years, Apple has tried to make the experience better, with features like Today, but the company has never quite understood the process of discovery. The Today tab seems to be the same for everyone, regardless of their interests. As I am writing this, for example, I am being advertised a category called "Texting for Tweens" which has no value to me as a user. In addition, the apps being featured are all products that the majority of people already know about: Hulu, Netflix, HBO Now, Prime Video, etc.
This behavior is the opposite of discoverability: it is just featuring of already successful apps. Thankfully we have the Affiliate Program to help promote apps that you don't already know about. That is, until October 1, 2018, when Apple will be removing apps and in-app purchases from the program entirely. This move on Apple's part is likely to cause app-centric websites to have revenue issues, meaning many of them will close. It will be a big hit to marketing for new apps unless Apple's claims are to be believed.
In a letter sent out to current affiliates, Apple claims,
With the launch of the new App Store on both iOS and macOS and their increased methods of app discovery, we will be removing apps from the affiliate program.
So, Apple is working on something new in the App Store to promote discoverability. The App Store on the current iOS 12 beta does not have anything new or exciting as part of it, so either the new features will not be previewed ahead of time, or it won't launch until the new devices are announced later in the year. The latter would make sense, being as October tends to be iPhone announcement time.
This does serve as another reminder that building a business on someone else's brand is always a dangerous idea. When the company changes its priorities, you can lose your entire business, as these app discovery websites are unfortunately about to discover for themselves.