“Double down” comes straight from blackjack, where you double your bet in a...

https://ericksimpressivenews.cavandoragh.org/the-best-way-to-practice-new-english-idioms

“Double down” comes straight from blackjack, where you double your bet in a risky move, hoping the next card saves you. People often confuse it with “redouble,” which is just... doubling again. Use “double down” when you commit more, not when you back off