If you need security and privacy in its highest order, then go for a decentralized means of storage, using a centralized exchange will intrude into your private informations, they can be hacked or turn a scam ad government can regulate them against your wish.
Neither centralized or decentralized exchanges should be used for storage, whether you care about privacy and use a decentralized exchange or you don't care about that and you use a centralized exchange, your funds should be moved into your self custody wallet after trading, wallets like Electrum, Sparrow or BlueWallet.
If DEX is superior to CEX, why do people still trust CEX more? Even if there are some big whales holding a large amount of bitcoin, they will choose centralized exchanges as the place to sell and not a decentralized exchange.
People don't trust centralized exchanges more, they know their funds are at risk of confiscation whenever they trade in centralized exchanges, but people use centralized exchanges because it was the only type of exchange they were introduced to when they started trading crypto, so they now find centralized exchanges more convenient. People will trade large amount of BTC on centralized exchanges just because of they have more liquidity.