In fact there were some cases which proves that you are wrong because there were some bankrupted casinos but of course the reason is not only because of player's big win.
A new casino with less experienced owner might be bankrupted because of wrong management for the bankroll.
Although the chance for casinos to get bankrupt due to big wins by player is so small but chance is still a chance that may happen.
To avoid this, casino need to have proper bankroll management which is the most crucial part of the casino.
I've read a lot of comments on this thread. It is unlikely that the casino will go bankrupt because many gamblers win the jackpot. The chances are even greater that the casino will go bankrupt when there are no gamblers. I completely agree with this, I think casinos are just like any other company, and all companies go bankrupt when they have no customers.
But a new casino that has bad finances can also go bankrupt, but it can go bankrupt because its operating expenses are greater than the sum of its revenues. In my opinion, the casino business requires large promotional costs to get gamblers to want to play there. Especially if it's an online gambling site, there aren't many choices of advertising platforms that allow gambling ads. So it costs a lot for advertising. When they have spent a lot of money on advertising, but their customers are still small, they are likely to go bankrupt