Perhaps because Nyma is a good sport and allowed the rematch (assuming these allegations are true)? Or are you suggesting that, for example, people who let their opponents switch marks after accidentally not switching aren't allowed to - even in the interests of good sportsmanship?
Unless Nyma has made this complaint herself I think the result should stand, since Nyma conceded the match in the first place.
About that Mark example.. if you ask my personal opinion, then here it is. Lets say my opponent had a great starting hand, but I had the wrong mark because I was dumb enough to not check my deck before we started. I don't think that it is "good sportmanship" to restart the whole thing because I have failed, possibly giving him a horrible starting hand, with which he will lose. That could potentially lead to a situation where
he would lose because I made a mistake. I think that is just wrong, and it's the opposite of good sportsmanship because it gives the other player an advantage he didn't deserve.
Making a mistake and using an illegal deck in War is an automatic loss. From a philosophic standpoint, I see no difference with that and closing the browser window by accident. Both are accidental losses caused by a mistake made by one person.
I personally feel very strongly that actions should have consequences, and it's the responsibility of the individual to make sure mistakes don't happen. And if mistakes do happen, it's that individual who should carry
full responsibility for them. I don't see how the opponent could be blamed for not being a "good sport", or the organizers blamed for being "unfair", when they had nothing to do with the failure happening, and in opponents case, being a "good sport" might lead to a loss.
The evidence against life in this match is fairly incriminating. If we give Nyma the win for one game and not the other it isn't fair at all. Either she gets the win for both matches or neither.
That means our two main options are to A) Give the match to or B) Redo the match in its entirety.
I think those both are excellent choices. I personally would go with option A, but for the masses, a more "fair" solution might be option B. If there is any doubt about what really happened or how this should be handled, doing a rematch and letting Elemental Gods decide, is always a good option.
It's your call.