I absolutly agree with you, but usually hackers hack the things that are less protected. And were there is a lot of money. That is why cryptocurrency exchanges are hacked very often. A lot of money and not strong protection.
I have not heard that cybercriminals have hacked online exchangers. But they regularly clean the crypto-exchange exchanges, because now there are many rich traders selling coins.
It seems to me that this is the case with exchangers because they change their wallets for each tariff plan. One exchange, one wallet