Not storing your bitcoin in an online exchange is what people should do or what we should recommend especially to newbies. As what op name is "not your key not your btc" explained a lot already. Think about accessing the wallets that contains BTC without the private key or seed phrase is impossible to do so that's why not your key not your btc is a good saying when it comes having some btc in a wallet.
Sure, it is secure for everyone, but sometimes certain individuals require a more flexible system for easier access and trading of our assets. In truth, all methods of storing Bitcoin securely still carry a slight possibility of being hacked. Hence, being overly possessive of our assets is certainly not advisable.
I am not advocating for asset storage solely on exchange wallets, but it is essential to maintain a portion of our assets on an exchange wallet in proportion to our sufficiency. It doesn't need to be substantial; the key is to have it. Personally, I often keep a balance ranging from $10 to $30 in a wallet that I can easily access for the purpose of purchasing something in case I forget to bring my physical wallet or if my balance is insufficient for shopping. You never know when such situations might arise.