I get in my car. The weather app is suggested to me, because I oftentimes, when getting into my car, want to check the weather. This is innocuous; definitely not an ad.
I get in my car. Candy Crush 2 is suggested to me, because I oftentimes, when being driven around by my wife, play games.
At a surface level, one could argue: Candy Crush did not pay for that impression, its not an ad. On the other hand; Candy Crush does pay Apple 30% of every transaction in the app; and that service fee includes not only access to market on the iOS App Store, but also, critically, access to be installed at all on iOS. Developers pay Apple to be allowed to install Applications on users' phones; any installed application could be given preferential display by iOS in suggested applications, location based suggestions, etc; Apple has a monetary interest (30%) in suggesting applications which would generate revenue for both them & the developer; the algorithms which power these application suggestions are black-boxed and poorly understood by consumers.
Similarly; I drive up to Starbucks, and iOS displays the Starbucks application. The innocuous argument is: arrive at location -> many users open this app at this location -> presenting it is convenient. The "weirder" argument is: arrive at location -> Apple wants to keep Starbucks happy, in the App Store, and using Apple Pay -> presenting it is monetarily beneficial to Apple & Starbucks, Starbucks knew that their app could be presented like this and approved of it, and thus its an Ad. Critically, there's nothing different about these two situations beyond intent, and to some degree that just speaks to the fact that we live in a capitalist society. But I label the situation "weird" for a reason. And "weirdest"? Arrive at location -> There's a starbucks & a panera bread right next to each other -> iOS can only recommend one application, so which does it choose? This is where being explicit about "this is an ad" actually matters; its no longer a matter of convenience or "wow that's cool", its a matter of "a billion devices are now pushing their users to make getting coffee at Starbucks a little bit easier than Panera", and that's not ok even if the intention is totally ethical.
I think there's an argument, maybe not a strong one but extant nonetheless, that any "preferential display" iOS exhibits toward one app over another, anywhere on your phone, is advertising, simply due to how intertwined their megacorporation interests & reach is with how money flows through their platform.