The casino in this case is the provider of the gambling venue and also the dealer. If you say that the casino never loses, you are wrong, the casino will also often lose, especially if more and more players win the jackpot, they will run out of capital, then that is not arbitrary to open a casino, if you don't have enough capital then throw away your desire to open a casino, but if you have a large capital to open a casino business then just do it.
Indeed. Just like other business, casino can also face losses and that is when many gamblers are hitting a jackpot (as you've said) and it's a problem if the casino can't sustain this situation. The reason why it is crucial to have a decent capital before starting to build your own platform (or any kind of business).
On the other side, due to house edge, casino has an advantage against the gamblers that's why gamblers are losing than winning. One of the reason why for us gamblers it's important to only use what you can afford to lose since winning is not guaranteed and it can disappoint a gambler if you have high expectation to win.