One consequence is also true that someone cannot or do not move their coins due to the fact that they have the money there due to their trading habits, and one major reason for which they do not move their coins out from the exchange is the fee they are charged every time, so they keep their money to fulfill their greedy habit of their everyday trading.
In this case, we should choose the right exchange where to entrust our money.
One of the reasons why they don't move their coin into non-custodial wallets is that there's a fee for every transaction they have, but isn't really a good idea to let your coins sleep on the exchange wallet.
I think that's not a greedy habit, looking and finding a way how to save fees is a wise move.
That's why when an exchange gets hacked or compromised, they freeze all accounts and didn't allow users to withdraw their funds. It will surely be really frustrating that will others will create a massive panic. Then, it's us who will suffer when there's a security breach on the exchange.