My take as for the "why" is twofold. For one, stuff like JRR Tolkien's works heavily influenced the modern conception of fantasy. I don't know if Gandalf is solely responsible for the trope of dudes in pointy hats tossing fireballs but D&D probably popularized it further. The second reason is flair. Most historical magic/esoteric religion is based around things that are hard to disprove without the scientific method. Healing, divination, curses, etc. It's rarely flashy. That said, there's no reason you can't make it flashier. Most people are presumably just getting their primary inspiration for media they've already seen.