By knowing the risks that will be accepted and the consequences of betting large amounts, they must also have spare money to be able to bet if the first bet loses and the money is lost.
The reserve money will be used with the aim of betting again to be able to win it and restore losses from previous losses.
If we follow and pay close attention to how the rich people play or bet, it will be difficult to understand because they bet using their logic based on a large enough capital that no matter how they do it they will continue to win.
If the rich will gamble with huge amount in order to win and make money, I'm sure all of the casinos already bankrupt since their bankroll are empty due to whales. Technically martingale strategy will work, but you need to have unlimited money because you're need to accept huge lose. But it's impossible because even a rich person does have limited money. i think most of high roller lose their money because they're get tricked by gambling tools about martingale strategy calculation.