A rules-only stack works one way: your analysts see a new tactic, write a rule, deploy it. Between the first fraudulent transaction and the rule that finally stops it, every copy of that tactic gets through. Meanwhile the rules already running are blunt, so they decline good customers by the thousand, and your support team spends its day reversing those declines instead of chasing fraud.
An ML model scores each transaction against patterns learned from your own data, in milliseconds, before it clears. It catches the variant of a tactic no one has written a rule for yet, and it routes the genuinely ambiguous ones to a human analyst rather than declining them outright.
The rule always ships on Friday. The model was already watching on Tuesday.