Re:Because that's what you wanted (Score 1)

I'm pretty sure you already can... There is a thing called PWA - Progressive Web Apps - that is supposed to enable you to do exactly this. I don't own any Apple device so I can't confirm it for 100%, but it's supposed to work there. Definitely works fine on my Nokia 5: if you're on a site that is actually a PWA, you get a prompt to add it to your home screen. After that, the app could even run offline (well, most web apps will want to show you some up-to-date content, so their offline capabilities will be quite limited, but something like calculator is absolutely doable as an offline PWA).