It's a continuous business, so making money will be unlimited as long as they can preserve the greatness of their venues.
But these guys didn't really start their business by making money at gambling first. Correct me if I am wrong. There are loads of stories about people who won in gambling but ended up in a different industry.
A strong example is the founder of the FedEx company.
In the early days of FedEx, Smith had to go to great lengths to keep the company afloat. In one instance, after a crucial business loan was denied, he took the company's last $5,000 to Las Vegas and won $27,000 gambling on blackjack to cover the company's $24,000 fuel bill. It kept FedEx alive for one more week.[13]
https://en.wikipedia.org/wiki/Frederick_W._Smith#:~:text=In%20the%20early%20days%20of,the%20company's%20%2424%2C000%20fuel%20bill.
He was not really a professional gambler but luck visited him and kept his company alive. It's not a recommended behavior but somehow it made a good story right now.
The guys you mentioned though really made it to the top by staying on the business where they are good at or maybe they just really love what they are doing so it's best to stick with it. Nowadays, it's difficult to do that. We are forced to do other labor, the ones we don't really like for the sake of money, and to live.