It is precisely because of online gambling that it makes no sense to try to keep gambling illegal, before online gambling was a thing someone which wanted to gamble would need to find an underground casino and be in company of people which most likely you would not want around you, but now the only thing you need to gamble is to have a computer and Internet access, and if you also want to retain some level of privacy you could get some bitcoin and then gamble with it, so those governments which are against gambling need to think again, as they are losing a great deal of revenue by having this attitude that does not make sense anymore in a world that is interconnected.
In the countries where gambling is ban - for them it is ban - if any government would try to legalize it they will face a backlash.
So government try to play save. Because for the community No Gambling means No gambling at all even if it brings huge profit. The call is the money earned from the gambling -- not Halal.
Countries that banned gambling wouldn't ban it for no reason. I'm sure that they have huge reasons for banning gambling in their country regardless of the huge taxes that they could get from it. Once they ban it, I don't think they aren't firm with their decision. Banning also has pros and cons in each country and I'm sure that the government focuses on the cons that made them ban it.