Rage is why Blood Elves are the only class that can't be warriors. The ability to instantly generate rage would have been overpowered.

The tauren forms also all have features unique to the race (horns, ears, coloring) and those would either not make sense or require more models to be used.

Other than that, the only real reason is lore I think.

Oh, the reason I'd heard for BE not getting Warriors was also pretty lore based. I read somewhere someone from Blizzard explaining it, saying that they didn't want to give BE more than 6 classes, and had to decide between Warrior and Hunter for the sixth class (because the light and magic classes were shoe-ins, and I guess they must've felt Rogues were necessary). They decided they couldn't in good conscious not include Hunters, as there's so much lore on elven rangers and what not. So, no Warriors for the BE.

The thing about rage generation does make a lot of sense though. I could see that being a little overpowered.

Pure flavour!

Blizzard wated the races to ahve certain feels to them, certainyl there are laore reasons in soemc ases but, for example, there is no reason that a Belf warrior can't exist. In fact many do, in the game, you just can't play as one. Human Hunters too,etc.

You'll find this is the case for many of the more believable class/race combinations that aren't actually available to be played. They can/do exist we're just simply not able to play as them.

Think of it like this, when you look at a Belf in game, you know what classes it can be, essentially, it'll be a mana user.(If it's your enemy your not likely to see a rogue coming if they're any good) this is very much the flavor Blizz wanted to give player Belfs. At the end of the day we know a Belf is more than likely going to be a ranged DPS unless they're in plate. The same philosophy extends to the other races/classes where the "lore" doesn't negate reason. It's like we're filling the role for how Blizz thought the races would be populated in the "real" azeroth.

Also it's another reason that gives racial selections at character selection a reason for existing beyond aesthetics.

I think the reason you won't see a gnome priest, is lore as well. Gnome's don't generally believe in a higher power, and since the healing classes draw on some sort of spiritual force to heal, the gnomes just don't get it, they are pure science.

I did read something a while back about a "hero-class healer" that would base its healing on scientific methods, or some such mechanic, completely out of the realm of spiritual-ness. :)

One thing I remember them using was "Belfs are feeble little pansies, and hence can't lord it around in plate armour." 'But what about the Belfadins?' I hear you cry. Well, what they pulled for them was "All that juicy Light magic goodness they nabbed off M'uru is their power generator to lift their Pinkadin Armour and Battlehammer of Questionable Pwnage". So yeh, Belfs too puny for the brute strength warrior plate class; agile ranger/thief characters suits them, priest/warlock/mage equally so.

Actually game balance itself was equal with lore in the decisions.

they wanted to have an even number of races for each class per faction now since then they have... branched away from that a bit, but it was originally intended, for instance if gnome's could have been priest (which would have been awesome) then the alliance would have had 3 special priest racials, while the horde had only 2. originally dwarves were considered as mages (which also would be awesome) but then there would have been more mage capable races on alliance than horde. so its all balance + lore really. i'd wager balance came first, then lore was applied, and sometimes overridden.

look at night elves, females should be the only warriors and priests, and druids should be male exclusive, but ultimately balance and player freedom in that case trumped lore.

please pardon my lack of punctuation above :(