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

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

"Double down" comes from blackjack, where you double your bet after seeing your first two cards to maximize a strong hand. Learners often mistake it for merely trying harder, but it’s about taking a bigger risk when the odds look good