Why do we usually see only one person using a type of magic? Look at Cana's magic for example. Out of everything shown via the Anime, no one else has used it on their own. Same with Reedus, Makarov, Evergreen, Bickslow, Gildarts, Jura, Erza (Knight), and many other people.
I can understand why limited number of people use the rare/lost magic (Dragon Slayer and other lost types), but what about the more modern magics?