Alot of newbies make this mistake of considering exchanges to be their wallet that they trust them to store their crypto coins for them but that's a big mistake that alot of them end up making.
It's lack of knowledge that makes many newbie investors mistake an exchange account for a wallet. Many of them were introduced by others who as well lacked the right knowledge on how to store their coins. So it becomes a problem once there's a root. Most times trying to teach such person would become difficult because they believe that the person they had learnt from, would know more about storing their coins.
Exchange offers it's user an account and a means for them to request for their funds anytime they so wish, but they literally are in charge of your coins and if things goes south, they may decide not to hand them over to you. So it's better to get a wallet and store the keys your self...