Why on earth would vulp and mech gnomes have a warlock mage or monk classes?
I know lore is kinda on the fly since Au wod but cmon man.
Something something, cute adorable fox wanting to steal your soul in more ways than one.
The easiest answer to that while all Paladins play the same, and all Priests play the same, the actual path that each race of those class takes is different.
For example, Troll Paladins worship Rezan and are empowered by him. Human, Dwarf and Draenei Paladins worship the Holy Light. Tauren Paladins worship the Sun.
Likewise with Priests, you’ve got Troll Priests, who serve a Loa (IIRC Darkspear typically serve Bwonsamdi), Undead Priests are part of the Cult of Forgotten Shadow (and mostly don’t use Light, either), Night Elf Priests worship Elune, and of course Human Priests are part of the Chuch of the holy Light.
But all these classes play the same, even if they have different roots, and probably would use their powers differently in a canonical setting.
Likewise, with Mechagnome and Vulpera, they might already be proficient in hand-to-hand combat, or throwing fire/shadow, and they might do it in a different way to other classes (especially those with established schools/covens like Warlocks, Monks and Mages), but it’s just easier to group them in with every other Mage, Warlock or Monk instead of trying to make them into some unique class.
I think they put on blind folds, pick up a few darts and aim at a dartboard. this is how classes get “picked”.
Then they turn to the writers and say make this work. doesn’t have to work well…just work.
Being nice they need to give races a mix of melee and ranged. So I can see the ranged options they have somewhat.
Monks I gave up trying to find reason there.
Even mech gnomes rogues make 0 sense i mean “clink clink” hmm who goes there?
Zip it and give me paladins!
Well, Mechagnomes have their lineage dating back to the Gnomergon Gnomes (they split off ages ago, but they are a split off culture) so them having at least Warlock and Mage could be justified in the same way Goblins randomly have those classes. Vulpera just have whatever Blizz wanted them to, since their lore is so bare bones atm that they are sort of running of pure personality and aesthetics. As for why both races got Monks? Cuz reasons. Just pretend a traveling Pandaren dropped by and taught them the basics long ago.
Maybe the mechagnome rogues have nano-tech sound dampeners!
rogues now have “power lifters” so yeah…sanity left the building way back here.
2 guards on patrol. 1 goes to the other…
You hear something?
Shhh, its the KT rogue. I feel bad for them. their gut casts a really big shadow and you hear every step they take since so heavy. I let him think he is doing a good job “sneaking” by us. Helps build his ego.
The less it makes sense the more chances I have at an orc paladin. 
Lightbound crusades expansion its on the way.
The Pandaren Monks are willing to teach literally anyone who’s willing to learn.
As for Mechagnome Warlocks: Gnomes can be Warlocks, so no issue.
As for Vulpera Warlocks: Since the Alliance sent Warlocks to set the Vulpera on fire they probably learned it while being burned alive or something.
I see it as both these races are starting fresh. They were basically isolated and have mostly non martial societies. Essentially they are blank slates and are learning everything from us and these classes are the ones we are willing to teach them and they are willing to learn.
They are monks, warlocks and mages because there were monks, warlocks and mages in the Horde and Alliance willing to teach them.
It’s been confirmed for a while now that stealth is a type of shadow magic not just people being sneeky. The this race can’t be rogues because they can’t be quiet argument needs to die already.
Warlocks and mages make sense for both. Mages use the arcane, which is essentially math and science made manifest. Both Vulpera and Mechagnomes can have an affinity for math and science. Similarly, warlocks use it, but the chaos / corrupted version of it. Which is fine too.
I agree monk is wonky though. But I think it’s because every other allied race can be a monk minus LFD.
I would like to know when cause I’ve yet to see any locks anywhere except void mages anywhere.
During the Voldun invasion event, the Alliance sends 7th Legion Warlocks to set the Vulpera on fire (WQ: Vulpera for a day).
Figured was a dwarf those poor foxes 
Every class but DK and to a lesser extent DH can just be learned/taught.
There are Humans too.