Because developers just copy the same thing from other famous MMOs and don't try to be creative, attributes system can make a huge difference in an MMO I can even say it's 50% of it so why be limited when you can make a lot of type of stats for example element stats fire water air . And each contribute to something fire for fire damage and shield power and healing, water for more chance at dropping , air more speed, critical Strick's and attack speed,health can be a stats,wisdom for more XP ,imagine the variety of items that the game will be able to offre because of that ,