Not just gambling, all the business should be opened with extreme care following the precautionary measures. Some business like gambling are not so essential for the daily life and can be delayed some more time before opening them.
Not if the governments need revenue and it is the one running the casinos like the casinos here in our country, in fact, it's one of the establishment that allowed to open, they want the cash coming in and they want the employees to get their paycheck so the government will not sustain them and of course, they have a lot of clients waiting for their opening, these clients are those who can afford to gamble, as long as they follow strict protocols they are good to go.
Still the government needs revenue during this pandemic if the casino company has a license then it will be opened by following a very strict protocol, I am sure this must be a lot of enthusiasts because now many people are bored, so if the casino is opened again, the client will automatically enter to play. as long as it follows government regulations, in each country the casinos are permitted and some are not depending on their respective regions.