Plenty of businesses are happy to block 20% of real customers to decrease fraud rates by 80%.

Especially low margin businesses, where you might have revenue of $20 in a transaction, but a profit margin of just $0.20, fraud is really painful if you lose the complete $19.80. You're happy to turn away a lot of custom to avoid some fraud.

Classic example: Bank loans. They might only earn 1% of the principle, so a fraudster who runs away with the whole principle has to be really rare.