I think both the multiple app store and 'apple isn't responsible for promoting your app' are both red herrings. The issue is that the search function in the app store lies to end users. To use the example in the article, if I go to the app store and search for "weigh loss tracker" I get 5 result, none of which is Happy Scale. The default sort is 'relevance', whatever that means, but i can change that to Most Popular. Still no Happy Scale. If I search for "Happy Scale" i get no result. From my perspective as an end user of the App Store, I'm being lied to. The search is not returning honest results that correspond to what I search for. This is not what the end user expects of search, they expect true organic results based on what they searched for, or at worst, a complete list with the apps Apple wants to promote at the top. In this case they are getting a curated subset of those results and not being told this is the case. Also, consider that the app store is unusable without search. There are million of apps, so is no way to browse it to find what you're looking for. If search doesn't return it, it might as well not exist in the app store.

Unless this is thoroughly explained somewhere in the dev documentation, then developers are being lied to also.

People threw a fit when Google changed the search result UI so that it became impossible to tell paid results from organic results. This is similar but worse. Google just put the paid results above the organic ones. Apple completely removes the organic results at their whim.

The author should have been promoting the app thru multiple channels and not relying on the app store search exclusively, this was an obvious mistake. This doesn't justify what Apple did though. It's their app store, and they can do what they want, but this, although legal, is pretty sleazy IMO.

Is this bad faith or unbelievable incompetence on Apple's part?

It's tempting to assume the former, but I seriously suspect the latter.

As a user I've seen this happen repeatedly. Search can't find an app even if I enter the name.

This happens for mundane but specialised apps - train timetables, toll payment apps, and other apps for which there is literally no alternative, never mind one that might somehow sell better and make more money.

I don't see how this possibly benefits Apple. Possibly there's some not very effective "optimisation" happening, but it's also possible search is just plain broken.

I'd argue this is a consequence of a lack of competition. Since there's no where else for you to go, what incentive do they have to fix search? Devs may complain a bit, but Apple still controls enough of the phone market that people are going to continue to make apps out of necessity and Apple will still get paid. As long as people can still find the "big" apps (uber, netflix, tinder, spotify, etc.), there won't be a meaningful outcry from users. It's not like someone is going to switch OS's over this.