Because it allows full character customization so I can make character types I don't often find in other games. Like my biggest example is Black Mage Archer. I love archer characters, I love black mage characters, but they are very rarely combined. Archers are usually not that magical and Black Mages usually are close distance staff fighters when they don't use magic. So for games like this where I can customize not only what abilities they have but what weapons as well I can have a black mage archer. And a time mage gunner. That type of thing

I'm a huge fan of games with set job classes OR freedom to make my own. I prefer making my own but I'll accept set jobs classes as a second best. What I don't really like as much is the middle grounds where everyone kind of has some of everything