Novel slavery...

Then why didn't the other races come together to fight a common enemy like how human is.

Like during world war 2 when most of the world unite to fight Germany and Japan.

Did they really that arrogant that they cannot see that they are being oppressed and just watch at the side. 

It´s because humans breeds like rats and therefore our territory of a world would be very high compared to other races. Sure, a single man would loose against a dwarf, elf whatever but humans don't fight wars alone. 

Not if they evolved in a static environment. Then rapid changes happened and their way of life worked only in certain places, like deep in the woods. There they remained traditionalists because it still worked.

Then change caught them slowly, like how you boil a frog. And now they are a proud race of slaves. 

Classic demand promoting the supply 

Depends what age we are talking about and whether or not the beastkin is herbivorous.
Herbivorous beastkins are as you said are the most likely to survive by far!
Carnivorous beastkin on the other hand are in much the same state as that of a human. However when they reach maturity their aggressive natures is generally their downfall.
Elves are equally fucked as humans as they generally are similar to humans if maybe a bit stronger/faster/magical however at the age we are talking about he elf is screwed.
Human is screwed.

The group who progresses the most is the elf. Elves have a natural connection to the forest only rarely generally they are able to create a niche where they can survive within the forest however don't have to destroy everything and respect everything whereas humans destroy and burn everything down! Humans have the easier job. However the elves stagnate cause they can't make more destructive stuff or they will have to rapidly change how they live. 

I haven’t really thought about that. In novels that I buy at a local bookshop, usually the elves and other races are usually above the humans on the food chain. While the novels here, as you said, they get enslaved. Maybe it’s just a cultural thing? Idk 

hunger and restraint imo just secondary or rather side effect from main problem
it may come from war with other factions or something like prisoner
on I forget which story bug I mean goddess favours human while nerfing other.... on rabbit story intervention from earth made human faction have superior technology so war with other faction become relative easier which made human feel superior race and other race just slave one 

War. When defeating and subjugating an opposing force, you eliminate the strong, the smart, and the rebellious leaving behind the defenseless. Then these defenseless are subjected to generations of oppression that cements into them the mindset of inferiority and subservience. Until it reaches a point that the status quo of repression is all they know and they could never imagine anything else.

At least until a figure appears that knows that there can be other ways and leads them in an uprising. Kinda like how the Hebrew were enslaved to the Egyptians until Moises, a figure who did not grow up as a slave, inspired them to escape.