If you used a bit of common sense and research, you would know why. Worgen and goblins don’t fit the class because of their nature alone, former is a savage animal with barely any self control, kept in check by a powerful artifact, but inside, in spirit they are fury incarnate which goes against the monk-ish ideals, which is all about complete harmony in body and soul. As for the latter… Why would a greedy race that only cares about money, become monks, point being, in goblin words - where’s the profit?
As for Worgen DKS, it has been explained in the past, in lore, that those immune to ‘‘undeath’’ alive, their corpses can still be raised and twisted as pleased. War of the Spider is an example, like worgen, those nerubians were immune to plague that turned others into undead, but when they died, their bodies could be raised into undeath regardless, hence Azjol Nerub, Old Kingdom…Anub’Arak, the crypt lord.
Probably the only inconsistency in the whole Worgen DK scenario is when you kill your former ‘‘friend’’ inside the building, i believe it talks about GIlneas which was walled off at the time of Arthas raising the player DKs, it would make more sense that the worgen came from areas surrounding GIlneas, like the sons of Arugal
Trolls have a racial ability called Berserking, which is the most intense form of rage. Orcs have a racial thats literally called Blood Fury.
Both of which are rare circumstances, it is not their natural state, both races are quite spiritually peaceful, orcs more than any other, given that large portion of their race is shamanistic.