Therefore humans are the most interesting. I mean, seriously, if you want to explore the human condition, humans are the way to go.
This is entirely your subjective opinion and it suggests you don't actually understand what I've said about story telling and character representations.
The 'interestingness' of a character lies totally and completely in the depth of Character (The writing/motivation/etc). Human can be just as interesting as a Goblin can be just as interesting as a Dwarf, if the story is interesting. Every single story that exists is a human story in the sense that stories are about brothers, about adversity, about love, about loss. If you are only interested in playing a human fine but I'd suggest playing any plethora of games out there that only have humans, like Mirrors Edge or something and avoid the Fantasy genre since the various races are an aspect that a lot of people find fun and interesting.
(Edit: Dwarves tend to represent the industriousness of humans, Elves tend to represent the loftier ideals and goals of humanity, Hobgoblins represent a militaristic view of the world, etc)
And it is entirely accurate to say it would be easier to add a type of character to the game if the models already exist as a portion of the work has already been done as opposed to a character that would need to be made from the ground up.
