Why are Apes size Large?

[kaomera]

So dwarves are kinda like very small apes?

Nah, dwarves are much too hairy...

 

[AbeTheGnome]

If the ape were measured as a quadruped, it would have a given length, not height (like the baboon). A 10-ft. reach for a gorilla is downright unrealistic. To make a gorilla, make them Medium with 5-ft. reach, maybe Powerful Build (I'd be inclined to give them a dwarf's bonus vs. trip and bull-rush instead), and a slam attack instead of claws. If you want to remake Conan's carnivorous apes, I'd still say that Large size is wrong. 500 lbs. is the top end of Medium. 300-400 lbs is definitely Medium. The entry also does not list them at 8 ft. tall (the minimum for Large).

 

[darkon74]

Another thing to consider is that the player's handbook says that a Large creature is typically 8 to 16 feet in height, but as mentioned previously apes do have longer than average arms which in turn would give them a greater reach, which is likely extends beyond that of a medium creature.