Why? Simply because of the topic mentioned at the beginning of this article:
exchanges can be hacked and you can lose all your funds. Thing is the majority of exchanges have a centralised custody system, meaning that you don't own your exchange's wallet private keys. And what happened if you don't own your keys...? Exactly.
To summarize,
be sure you keep your funds safe. Whether it's on your private wallet, or trading in
the new generation exchanges that have a transparent custody system, meaning that only you can access your funds and they will be safe in case there's a hack to the exchange.
Tell me: What's your strategy to secure your funds? I have 2 choices when storing assets on an exchange
1) First, if the crypto exchange stores the assets of the trader in a centralized storage, then the exchange must return the assets of the trader if one day the storage has hacked and stolen,
of course exchanges like this have a clear team and have certificates from neraga
2) secondly, a decentralized exchange, which stores assets in centralized storage, if the storage is hacked and stolen then the exchange will not return traders' assets, I will not store assets on an exchange like this