Disclaimer: This excludes curses and things of similar nature as their functions aren’t entirely clear.
TL;DR: Because magic energy doesn’t exist in real life, using magic of that in the AU in real life is impossible.
To understand this, it’s important to note the existence of light and shadow magic. Now, light and shadows are non-physical, and so evidently would not be able to hurt you or damage objects as they do in this universe. However, any magic of any element (magma, fire, etc.) is really just magic energy imitating that element, hence why things like light and shadow magic can do physical damage. Light and shadow magic in particular also do damage as the magic energy imitating them reacts violently with the magic energy in an organism’s body, thus doing damage. How do I know this? Just trust me, bro.
Now, magic is utilized via “minds”, parts of the brain that allow for, well, using magic, and each mind is of a certain magic. While the AU is a fictional universe separate from real life, it still seems to obey relatively the same laws (aside from people having ridiculous leg strength). Energy can’t be created or destroyed, and the same goes for matter. To cast a spell, you have to cast magic, but to cast magic, you need to summon or draw that magic from somewhere. We don’t know exactly where that magic comes from, but we can assume it comes from either the atmosphere or oneself (as, again, all beings in the AU inherently have magic). Now, in real life, casting magic would be impossible, because there’d be no magic in yourself or the atmosphere to draw from!
“But, can’t we just manipulate our environment?”
Nope! Magic is generated through magic circles, and while magic a long time ago (referred to as primitive magic) didn’t require the creation of magic energy and instead drew from the soul, it still likely also required some magic energy to function. Anyway, magic is used through magic circles as a safer method, and wizards (source: trust) can only manipulate the element or magic they create. This is likely because inanimate and non-living matter doesn’t possess magic energy, so it can’t be directly manipulated. It’s possible to probably shoot a magic blast at a lake to make some water in it splash and thus “manipulate” it in a sense, but my point still stands. As such, it is impossible to manipulate your environment with magic.
So, if you could use magic akin to that in the AU in real life, you actually wouldn’t be able to use it, as there’s no magic energy anywhere in real life (at least, I think). It’s important to note, though, that this only concerns magic of the AU, and that magic of practically any other fictional universe would work in real life (except maybe Fairy Tail, I guess.) This also may or may not include curses as it’s unclear how they create their element (and because curses use the actual element itself rather than imitate it with magic), and because curses likely can grant one the ability to manipulate the element of the curse in their environment, not to mention external curses.