"Double down" comes straight from blackjack: you double your initial bet after...

https://kilo-wiki.win/index.php/Why_Do_Native_Speakers_Not_Notice_Idiom_Origins%3F

"Double down" comes straight from blackjack: you double your initial bet after seeing your first two cards, hoping for a strong third. Language learners often misuse it to mean “try harder,” but it specifically means committing more with risk