They aren't making as much as they used to make. Back in the early days there wasn't much in the way of regulations. US players could play just about everywhere - same with UK players, Australian players - everyone. So in the early 2000s, casino operators, especially Microgaming and RTG operators were making a shitload of cash.
As soon as the UIGEA was passed in 2006, loads of operators and software providers began bailing from the US market - which was massive at the time. And by 2010 or so, the US market began to seriously decline. At the moment, only a handful of casinos are still able to deal with the US market.
Australia - which was one of the biggest markets - was severed. No one can take Aussie bets or advertise for Aussies unless that want to get arrested at the AUS border.
The UK and the EU has seen more regulations when it comes to Source of Wealth requirements which has turned off loads of players, and with stricter rules, you won't find some players dumping loads of cash into whatever casino - which is a good thing for the player, but the casino is not making money there.
Now you have the Covid-19 virus which has shut down sportsbetting pretty much - so you know William Hill, Betfred, Paddy Power, Bet365, etc., etc., etc., are really hurting at the moment.
Some people are saying - well yeah, online casinos now will make more money now that everyone is stuck at home. But I'm thinking that in the next few months, disposable income is going to dwindle since many people are losing their jobs - especially in the service industry.
So in a nutshell, online casino operators don't make all that much - at least compared to what they made years ago.