That's true, a lot of people I've seen complaining about their exchange accounts getting compromised and their assets being stolen because they have been keeping all their assets in their exchange account which is a big mistake, someone should only keep a specific amount of money in exchange, the money that they use as their trading capital if they are making trades regularly.
If someone doesn't make trades on a daily or a regular basis, they should simply keep their assets in a non-custodial wallet where they will be the only ones to have access to them and no one can access them unless they leak their seed phrase or private keys.
To be fair, it's kinda hassle for some people to move in and out their funds between exchange and their wallet and to be honest back then, I was like that when I was day trading in Binance. After I learned the horror stories of people getting their funds frozen, I started to slap myself so bad that I would not do that every again.
It depends on what you use the exchanges for: if you do daily trading then you have to leave the funds on the exchange, there is no other solution. Is it a risk? Yes, of course. If you buy for the long term and you leave the funds on the exchange because you're lazy it's a totally different story. Personally I just leave on exchanges some shit coins, I would never leave a single satoshi.