I'd wager that it's because banks are able to reverse transactions, so even though there must be hackable banks out there (on account there being thousands of them), it must be incredibly difficult to monetize.
Additionally, if you hack a crypto exchange it isn't clear that law enforcement will be all that interested. If you steal from a bank, or from the people who've made deposits at that bank, it's a different story.
Lastly there's an infrastructure of coin laundries to facilitate crypto heists that's accessible to everyone, but in "tradfi" that infrastructure either doesn't exist or isn't generally available.
Additionally, if you hack a crypto exchange it isn't clear that law enforcement will be all that interested. If you steal from a bank, or from the people who've made deposits at that bank, it's a different story.
Lastly there's an infrastructure of coin laundries to facilitate crypto heists that's accessible to everyone, but in "tradfi" that infrastructure either doesn't exist or isn't generally available.