“Double down” comes from blackjack—when 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—when you double your bet after seeing your first two cards, betting you’ve got a winner. Learners often misuse it to mean “make more effort” generally, but it’s really about risk, doubling stakes