I can’t speak for other mages, but most of my horde mages are young, or have some form of reasoning to why they are a mage.
Kubluku, my troll mage, isn’t a mage, he has an enchanted ring that grants him magic powers that he doesn’t know how to control, and must roll against a table of random effects every time he casts a spell, ton of fun! He’d naturally have the ring confiscated or something, but he err… swallowed it, and it hasn’t quite come back into his posession.
Korenia here is the Daughter of my Warrior, she has been trained in magic because she’s named after my warriors sister, (Who’s still alive, but missing. Presumed dead, has been for a while.) So Korakk, out of worry for the first life he brought into being, insisted that she learn spellcraft. Korakk being a general, has seen great potential in wizards fighting alongside warriors, he can keep her close, without her risking getting wounded.
Not very orcish of him, but maybe all the fellow horde races he keeps as company have made him soft.
Kareva, my pandaren mage, is a party magician, But I’m guessing you wouldn’t count Pandaren as unfitting mages in your mages of the Horde. She conjures fireworks and dragons made of fire as spells.
Vodkah, my goblin mage, is a, ahem, a… Well, A lady of the night. XD I don’t ERP myself, (I don’t judge either, it’s just not for me.) so all her proclivities are whenever I’m not playing her. She learned magic because quite simply, sometimes, if you’re without any clothing, you still need some form of protection! She also enjoys setting stuff on fire, go figure. If anyone gets too rough though, her sister / bartender, Whisky (I’m real imaginative) is a warrior with a big fiery hammer. She’ll sort them out!
Zincha, my Zandalari troll, is quite old, and a learned scholar, a mage fits quite well into the Zandalari, being their ancient culture and thirst for power. She has abused time magic to sustain her life force, and typically uses fire (I hadn’t realised, I have a lot of fire mages, Korenia and Kubluku are the only non fire so far.) as a means of combat.
She however, does not approve of the faction war. In any of it’s carnations.
Zevrahel is Nightborne, so I mean, if he weren’t a mage, that’d probably be odd. XD (Yes, another fire mage, jeez…)
Hailana is a Blood elf, Frost mage this time, yay, not fire!
I think, and hope, that’s everyone, that’s plenty of Horde mages. I even have a bunch of alliance ones! (Some are Fire… Damn…)