The cultural disposition of humans in Thedas is to be the top of the heap, the dominant species, the privileged, or even the oppressors, that's something you can only play in DA as a human unless the game is set in Orzammar and you play as a dwarf noble. Taking away the human noble would mean that no one would get to play that kind of character. I do think any future human origins should be from a different country though, maybe Antiva or Nevarra.
I hate playing as humans, but you can only be a noble if you're a human so it gives me an incentive to play them occasionally.
This, pretty much. The whole point is that, as a human, you are
never truly at the bottom of the totem pole. You're a human living in poverty, struggling to find work and feed your family? Any elf or casteless dwarf in those same circumstances has it worse. People dig the idea of playing the underdog, but they don't want to give up playing the "best" race in order to do it. Loool
I do think certain non-noble human backgrounds would be very interesting, however. I love the Avvar. If we could be one of those I might actually bother playing a human for once.