Sometimes they are actually two sides of the same coin.
Some people are cynical just for the sake of it. They think naiveness is all about gullibility, and in this cruel world it could mean doom, so they go for the total opposite of naiveness that is cynicism. Or they just adopt the mindset because they think it’s a mark of toughness, maturity.
Ironically, by trying to stay as far a way as possible from naiveness, they come closer to being naive than they can ever dream of.
People who stick to blind cynicism is not better than a naive person. They totally miss out the complexity of life and a chance to grow. Cynicism becomes nothing more than just a label for the ego to gnaw at.