“Double down” comes from blackjack, where you double your bet after seeing your...

https://wiki-view.win/index.php/The_History_of_the_Blue_Chip_Term_Origin:_From_Poker_Tables_to_Boardrooms

“Double down” comes from blackjack, where you double your bet after seeing your first two cards, betting on a stronger hand. People often misuse it to mean “try twice as hard” generally, but it’s really about risk—doubling what’s already on the table