Why can't we play orcs or imp ? Lack of time / money to add it ?
Yes, at least in part. There was an imp princess started for Dragon Commander, but there ended up not being enough time to implement the character properly before the release of the game, so that was cut.
With D:OS 2, each origin character added increased the dialogue and story more than the previous one (due to the interactions between the different origins). That limited the number of origins that could be added. Imps and orcs would also have taken more work for art and animations, etc, compared to the other characters, and given their history, to add them to the game properly would have needed many more NPCs to treat them differently.
