I fully agree that (A)GPLv3 code effectively stops code from being used by many large companies (every place I’ve worked in the last decade has a near blanket policy on refusing to use code licensed that way except in very specific and exigent circumstances), but it isn’t necessarily true that app developers can’t use (or can’t choose to license) (A)GPL code in their iOS apps, provided they abide by the terms of the license.
Most developers won’t — or can’t — but the advent of dynamic linking of libraries in iOS, as well as the EU-mandated third-party app stores (which aren’t available outside the EU, but still), make the situation a lot more grey from the black and white stands the FSF attempted to take in the early 2010s. And to my knowledge there have been no legal challenges about the use of GPL code in iOS apps, so the issue is essentially unsettled.
That said, in most of the cases where I have seen iOS apps use GPL code, the full app source was available (and that may or may not fulfill the redistribution requirements but I’m not a lawyer and I’m not going to cosplay as one).
On Android, where full Google Play alternatives like F-Droid are available, plenty of GPLv3 apps exist, even if they aren’t available on Google Play.
But yes, when it comes to incorporating GPL code into a non-GPL app, that is much more difficult in the realm of mobile than it is for other types of applications.
