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

https://wiki-cable.win/index.php/Gambling_Idioms_in_Business_English:_A_Risk_Idioms_List_You_Can%E2%80%99t_Afford_to_Miss

"Double down" comes from blackjack, where you double your bet after seeing your first two cards, aiming for a big win. Learners often misuse it to mean 'do something twice'—not quite. It’s about commitment, not repetition