When you have proof of cheating the sport's authorities take action (not individual players). When you don't you let the games go on knowing some folks are getting away with it sometimes.
If you look at FIDE's statement, they basically said they were made that Magnus did this and they're using "sophisticated" techniques to prevent cheating. I don't think that is a responsible way to act, given that this presents an existential threat to the sport.
With today's system, there is no way to get proof of cheating, without catching someone red handed, and there's no way to bring awareness because FIDE is either not interested, incompetent, or both. Also, there might be a lot of cheating in chess, and it could be just an ugly secret that they're protecting.
you assume that cheater is stupid and uses cheats for every move in every game.
If you use engine as a crutch to stop you from blundering and suggest moves that you understand, combined with adhering to steady but not explosive growth in elo points,you most likely end up undetected.