It’s not just that they don’t want it, it’s that they’re liable for it themselves if they should have known it was happening. Asking you adds one more small layer of “we discouraged illegal activity and we didn’t know about any”.
Bank 1 has the CYA clause and a cartel uses them for a decade for illegal purposes.
Bank 2 does not have the clause and a cartel uses them for a decade for illegal purposes.
In neither case does the clause prevent the illegal activity or make the bank any more or less aware of what customers are doing. They have to do KYC regardless of what the TOS says.
If you have actual measures (such as asking for source of funds and then asking for proof if the evidence looks incongruent with what was stated), you have no need for the silly question; if you don't, the silly question won't save you either.
This should go for both the asker and the subject of the question: Illegal things are already illegal. If a given legal system requires the silly question to be able to "tack on wire fraud charges" to something that would otherwise go unpunished(?!), I think what should be fixed is the legal system, not every single banking form.