Why Utawarerumono? It's because of the events that transpired in the game. In my opinion, the layout of the anime didn't quite explain it as effectively. You see,
Ahhh, wikipedia. You can spend a few days there and learn all kinds of stuff. It's actually a very helpful resource, but bear in mind that they're not 100% correct on some things (and their description of Utawarerumono, particularly its Background text, is no exception. Minor errors, but errors nonetheless).