No Consequences for Killing on Holy Ground
Maybe this was discussed in the earlier films or TV shows. I can't recall.
But Jacob Kell goes to the sanctuary where Connor and the others are napping...and slaughters them all. Even speaking aloud how he doesn't care about the game or the rules.
In the earlier films, I always assumed that something inexplicable would happen to an immortal if they killed on Holy Ground. Like their heads would just fall off on their own accord.
But in Endgame, there's no consequences for Jacob Kell at all. Why would any of them follow the so-called rules...if cheating gets you to the finish line faster? And no reason not to.