Just because it is something YOU want doesn't mean we ALL want it. I appreciate Apple's review of apps and their store policies. While no human endeavor is perfect it is at least an attempt to keep their platform more secure, safer for kids, higher quality, and more trustworthy.
Opening up the platform to other app stores means they have less control over the experience on their platform it opens more avenues for malware.
Why are Apple users so quick to recommend me Android when I point out this particular flaw with iOS? And yes, I do consider distrusting the owner's software installation preferences to be a flaw, especially when Apple is certainly capable of maintaining a robust and safe third-party distribution ecosystem on macOS. The Mac isn't demonstrably less secure because you have a sanctioned way to install Steam onto it. Likewise, Apple doesn't lose the ability to maintain the quality of the Mac App Store because people might get their apps on Steam.
"Safer for kids" isn't a factor here; Apple already provides tools for parents to lock down their children's devices should that be necessary. This would also presumably have an option (or default) to disable third-party apps, in the same way parents can already disable specific App Store and built-in apps.
> less control over the experience on their platform
I value the customer's ability to install programs of their choosing on a phone they purchased. It seems strange that we see it as desirable to concentrate authority over billions of devices this way. Taking a step back, it's sort of a "what could possibly go wrong" scenario.
Opening up the platform to other app stores means they have less control over the experience on their platform it opens more avenues for malware.
If you want a more open platform use Android.