Worgen History
Origins
Though to be accurate, the Druids of the Pack used the Pack Form - which draws on Goldrinnās power - during the War of the Satyr. This was the form of a four legged wolf. When they asked Elune for aid in controlling the form, it was her contribution that made them into wolf-men. While completely sane, articulate, and incredibly efficient in battle, Malfurion saw them as a crime against druidism and banished them to the Dream.
https://wow.gamepedia.com/War_of_the_Satyr
https://wow.gamepedia.com/Curse_of_the_Worgen
https://wow.gamepedia.com/Goldrinn
Gilneas
Over nine thousand years later, Archmage Arugal discovers these Kaldorei-worgen trapped in the dream, and Genn Greymane orders him to summon them to fight the oncoming Scourge. Unbeknownst to them both, the worgen are intelligent, clever, and powerful. They kill the undead outside the wall, bite several Gilnean soldiers, and take Shadowfang Keep. Archmage Arugal swears loyalty to Alpha Prime, their leader, and the worgen start The Wolf Cult in Gilneas, initiating and biting willing Gilnean humans. Gilneans who would later help them spread the curse - which they see as a blessing or āPurityā - through all Gilneas.
https://wow.gamepedia.com/Alpha_Prime
https://wow.gamepedia.com/Wolf_Cult
https://wow.gamepedia.com/Lord_of_His_Pack
Worgen Races
Humans and Kaldorei
Now, why exactly only Kaldorei and Humans can become worgen is up to speculation. Since the Pack Form was not infectious, Goldrinn is not to blame for the Worgen Curseās infectious nature. This factor only came with Eluneās involvement, and it seemed to be designed for Her favored children - the Kaldorei - from the get-go. But humans? Humans either earned Her favor, or are close enough physically and spiritually for the curse to work on them, the former seeming unlikely.
Either way, the worgen curse doesnāt just turn you into a random furry. It turns you into a lycanthrope. Elf or human means little, you become an eight foot wolfman regardless, both of which look identical ingame and in the comics.
Forsaken and Vrykul Worgen
In addition to the general human or elf that gets bitten, there are a couple other odd cases of worgen. One such being Apothacary Berard, a Forsaken Royal Apothecary, who was assigned to study Archmage Arugalās magic. In retaliation, the Archmage placed a curse on the undead man, turning him into a worgen. In addition, there is Selas in the Wolfcult; a worgen that stands twice the height of those around him, wields axes, and is in the Grizzly Hills
https://wow.gamepedia.com/Apothecary_Berard
https://wow.gamepedia.com/Selas
Other Races
As for other races, if they did qualify for the Worgen Curseā¦ Iād like to see Gnome-worgen and Orc-worgen. āGnomegenā is something some Gnomes are already looking into (see Quest: Worldās First Gnomegen) and Orcs already have a strong connection with wolves, and with Goldrinn, who they know on their homeworld as LoāGosh. Iād like to think Gnomegen would look like tiny wolfmen, while Orcs with the tusks - assuming they get to keep them in worgen form - would look fittingly like Worgs.
https://wow.gamepedia.com/World_First:_Gnomegen
Somehow, I canāt imagine any other races than that becoming wolf-ized, from an artistic perspective anyways. From a lore perspective, I would say the race would have to be arcane-based (like Kaldorei and Humans), be vulnerable to change, and cannot have been already adopted by a higher power (like Lightforged, or Void Elves).