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

https://www.inter-bookmarks.win/double-down-means-to-commit-more-effort-or-resources-to-a-risky-move-it

“Double down” comes from blackjack, when you double your bet after seeing your first two cards, hoping for a winning hand. People often misuse it to mean simply “try harder,” but it’s more about risking more when you think the odds are in your favor