If I remember correctly, XIII isn't a dream match game, so a lot of characters might have story line reasons as to why they're absent. Just throwing in whoever wouldn't work given the plot. I don't normally care about story lines in fighting games, but KOF is so plot heavy it makes sense. However, XIII is the end of a story line arc, and if patterns hold true, then the next KOF game should be a dream match, so everybody and their grandmother should be in it.