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

https://sticky-wiki.win/index.php/What_Is_a_Dead_Metaphor_in_Linguistics%3F_An_Insider%E2%80%99s_Guide_for_ESL_Learners_and_Word_Nerds

“Double down” comes from blackjack, when you double your bet after seeing your first two cards, betting on a strong hand. Learners often misuse it to mean “try harder” in any situation—nope, it’s about risk, not effort