A very safe exchange today can become a scam exchange tomorrow or it will collapse or bankrupt by any reason you don't know today.

Before FTX collapse and bankruptcy within a week, it was a Tier 1 exchange so it might happen with Kraken and other top exchanges. We can not know what they do behind the scene but if we are aware of this risk, and manage our bitcoin better such as in our non custodial wallets, we can secure our coins better.

Reminder: do not keep your money in online accounts.