It makes it less ambiguous. There is no suggestion when you enter the Apple ecosystem that there is any way to use 3rd party hardware or software.
There is one supplier for the hardware: Apple. One supplier for the OS: Apple. And for phones, tablets, TVs and watches, only one supplier for software: Apple's official store.
Apple hardware like a gaming console. You buy an Xbox because you want/need an Xbox. You don't start fantasising about installing Arch on it and playing indie games from itch.io. You're perfectly happy getting what's available in the official store.
Somehow, that is repeated so often as if it was the truth. Making both HW and SW makes it even worse, not better.