Ok little more about ethnicities in WoW. We have Trolls from what I remember(maybe retconned already) all trolls hail from Zandalari who live in particularly “prehistoric”(like Un’Goro) region of Azeroth then we have Dark Trolls(don’t know their Troll name) who lived in Ashenvale like zones(Fairy magic zone), then we have Amani who lived in European forest hills eqv. of EK, Drakkari who lived in Tundra eqv. and Gurubashi who lived in African Jungle eqv. All "evolved from Zandalari in different climatic zones. Then Gurubashi evolved even further in zones around Uldum, when they were turned into Sahara desert like and turned into Farraki.
Same thing with Elves Night elves evolved from BT in ashenvale like zones then some of them moved to EK europian green forest zone(took part from Amani) and made it bit more fairy like with Sunwell(still don’t get it tho why it so different from rest of Moonwells) - since zone was different and source of magic too they changed both colours and appearances, then they used Fel crystalls and slightly changed(duration was short tbh), then they got original magic source with a twist of light and slightly changed again(still short time). NB is kinda mess but still their originally NE zone was changed with Eye of Aman’thul(titan relic) radiation similar to Moonwell so they instead of changing colours changed their appearance to of NB partially like HE/BE did since well is different. VE changed by single person via cast.
Same climatic zone skin tone differences can be traced with Orcs in WoD although to a lesser degree.
Or Dwarves.
All gnomes lived in one place still there lepper gnomes from exposure to “Radiation”
Can’t say about Draenei since we don’t know how Argus looked like besides Mac’Aree. In Draenor they lived in one place mostly in one place besides outposts.
Lightforged were drastically changed by light way more than BE.
Grimtotem also different from what was their clan name again - default Tauren?
Highmoutain are base Tauren changed by Demigod.
Undead are not species(they cursed human corpses) so there is no point to even argue about dead Lordaeronians on different states of dicomposure.
Goblins is kinda of funny whenever they live they make place a trash dump so it does not matter which zone they live.
Pandaren hail from same zone.
Worgen are just cursed humans.
So what about humans from lore point they are not irl humans we are apes not magical elemental living beings. All human kingdoms exist in same time of zone European green forests with slight variation so majority them being white kind is given. But there another factor here technical one - when WoW was made it was made by Blizzard from modified WC3 engine and assets and it was Blizzard not ActiBlizz mega corporation with billions to make a game. So humans were one model with different skin tones and few faces wrapped on them. It’s easier to make Blue and Green trolls and call them different than do same with Human as they have direct real world reference. Now we have what always been in lore - some Azerithians lived in Strangle - african jungle that’s why there black people some lived in black moras(swamp of sorrows and blasted lands) asian wet jungles like vietnam - that’s why there asian people. Likely most of them have been fled to their Kingdom of Azeroth(one from Gurubash others from horde) and that’s why they presented there. Some people traveled Uldum and settled there(for whatever reason) and now there “Arabiiiaaaan Niiiight…” in Uldum(God I loved disney Alladin as kid). So I think magical humans of WoW change same way as other magical species kinda most prevalent element in climatic zone affects them over long period of exposure.
Lastly from game that is MMO and some kinds of Humans presented in setting reasonable majority of players should be able to create characters that resembles themselves for sake of escapism alone. That is unless there some lore that sets Human races differentiated(like Humans in ESO - Nords, Emperials ect.) which is not the case of WoW.