Unfortunately, Apple's own App Store Terms of Service don't allow use of GPL software on iOS.
https://www.fsf.org/blogs/licensing/more-about-the-app-store...
https://www.fsf.org/blogs/licensing/more-about-the-app-store...
The majority of Apple's stack is opensource, too. Take a look through http://opensource.apple.com/ some time. The kernel and huge swathes of their ecosystem are opensource. I'm writing this comment in chrome, which has millions of lines of opensourced webkit code in it, written by paid Apple engineers. And compiled in clang/llvm, which is developed, maintained by Apple. Oh, and its opensource too.
I'm totally confused by the argument that Apple hates opensource. They depend on it. They give back. They're a good citizen.
They just aren't huge fans of the GPL, but so what? Neither am I. Neither is Rust (MIT), or Golang (BSD) or the NodeJS community (90%+ BSD/ISC). Opensource simply doesn't need the GPL to bloom in today's world.
Open source is about collaboratively building tools for developers and businesses, or simply because collaboration produces better software. The software is often released under permissive terms. Apple participates in open source projects.
Free software is focused on the end user having freedom over their software by ensuring that they have the ability to read, modify, and redistribute it. Apple does not give these rights to users of their platforms.
The post that was linked was the FSF, which argues from the free software perspective.
https://www.gnu.org/licenses/license-list.en.html#GPLCompati...
Note that the BSD license, Apache license, MIT license (which the FSF calls the X11 license), etc. are all considered Free Software licenses by the FSF and are okay in the App Store.
If its not illegal, then perhaps it should be.