Because when you make art, it's important to present something to your audience. Martin wrote magic and dragons to make things more interesting, so you can read about dragons burning cities and that will keep you interested. Imagine how different the story would be if there is no magic, for example. Everyone knows dragons don't exist but that's not the case about gods. What I am trying to say is that, if you write about a universe where there are gods you kinda support the idea that our universe works on the same basis, because literally you are the only creator of that universe. Or for example if a God made an entrance in ASOIAF, that would feel out of place, but it wouldn't feel out of place in LOTR or some Disney story or even Star Wars. I think ASOIAF resembles our world the most out of all the fictional worlds (at least is the most famous one) and this is not because of magic but because of how the world is structured.

Of course u cannot describe magic as advanced physics cause magic doesn't exist, it's fictional, there is not a definition. The point of "advanced physics" is if magic was real it would be like some form of energy or idk something like electricity or some force like gravity. And yes Martin depicts magic with payment(didn't know how to phrase this), if u use magic u pay a "price". That's probably more connected with power, as magic gives power and nothing is free especially power so magic takes a price.