Because the you tube community etc who claimed it was tier 0 which it never was and the players who kept copying and flooding pvp with the same cybers over and over which resulted in the rest of us to easily find ways to counter this so now cybers have become inconsistent
Well, if you go against a mirror match, if you don't have a perfect CA deck and a lucky hand, you'll lose. If you go against other decks, you really on them not drawing counters to your deck, which they will most likely have, if you're in legend