I think online casinos are doing great. Of course financial situation has reduced their income, however they still grab a lot of money from gamblers. There were always gambler, there will always be gamblers. Infinite business I must say. While gambling, people seek to many goals. For example my post soviet country is filled with hundred if not thousands of small slots game rooms (they have proud name of a "Casino" lol). No matter how bad is situation in country, no matter what time is, they are always open. I am 100% sure that neighbour countries are also having such thousands slots game rooms. As to online casino. You just need a page, script, admin, some tech guys, and few more people like security manager. You dont have same expenses as offline casino. It is easier for them to survive, yet hard to survive competition.
Actually, I think they are gaining more than physical casinos.
It's just divided because there are many online casinos and sports bookies that opened up. But sum it all up, the money coming in will be much higher than the total of how much the old-school casinos are making. I don't have the numbers but that may be possible in today's era.
You are right, the expense of opening an online casino is not much for capital. They don't need a big space to rent, just need enough room to put in encoders, customer support, computer specialists, and marketing unlike physical casinos which also buy the devices for slots, tables for poker, blackjack, and it's maintenance.