Because red is a sexy color ;)
Jk, jk. It's all about utility. RDM has always been a class with reasonable melee DPS while also being able to use all but the strongest Black and White magic. You would essentially have a class that could get up close to deal some damage and then cast magic from a distance while being able to buff the party or raise people.
How it's probably going to work in XIV will be a balance between burning all your MP down then using TP moves while waiting for MP to regen so you can spam magic again.
