“Double down” comes from blackjack: you double your bet after seeing your first...

https://idiominsider.com/talking-odds-at-work-the-risk-idioms-every-english-learner-gets-slightly-wrong/

“Double down” comes from blackjack: you double your bet after seeing your first two cards, betting on a strong hand. Learners often misuse it to mean 'try harder' broadly, but it’s really about risking more when the odds look good