Originally Posted by
Andevom
Short Answer: Because of the playerbase.
The concept of a Blue Mage being able to customize their skill set, which is a big part of the draw, would be completely destroyed because people would ultimately dictate what the "correct" setup is for endgame. All those nifty abilities you've learned would be narrowed down to a handful, especially since they'd have to make certain abilities flat out not work against raid bosses.
This is a job created for people who aren't necessarily into that scene so they can mess around and have fun, while still working towards something without being told they're "doing it wrong". For everyone else, you've got all the other jobs at your disposal.