Everyone, because it simplifies Apple's maintenance efforts for macOS, iPadOS and iOS. The operation system itself is the application people run the most and now Aplpe can target the same silicon across the board. The M1 isn't just a faster chip, it allows for countless of efficiency optimizations developed for iPhone to be transferred back to the Mac.
That's obviously not what I'm talking about, if you read my explanations in the previous replies.
Even code to very different OSes can be ported if the company a enough.
What I'm saying is that the user is not really able to transparently execute MacOS apps in iOS, and iOS apps in MacOS.
Running iOS apps in MacOS is easier, but there are many reports of apps not working well with simulated touch.
The REAL problem starts when you want to run a MacOS app in iOS. It's just impossible UNLESS a developer specifically ports the app to the Apple Store.
Not only that, but by definition, there are apps that Apple forbids on the iPhone / iPad. They expressly forbid emulators and virtual machine software. Even though your iPhone and your iPad is perfectly capable of running virtual machines, Apple goes out of their merry way to block the hypervisor, which is a key piece to get a virtual machine running at full speed.
It's not that the hypervisor is not available. It IS available. But they actively block it, and it is only available through an exploit (or if Apple themselves use it).
Their effort to block emulators was for nothing though, because now there are browser-based emulators. Specifically, some now run locally, but in the browser. They make use of WebASM (Assembly language for the web). This results in code that is not as fast as native code, but that is obviously fast enough for applications like these. Since the code runs on the browser, it doesn't need to be installed.
Here is an example of a browser-based emulator:
https://afterplay.io/
Apple could go all their merry way to block it too, but in doing so, they would make their phones much slower and clearly inferior to Android.