The answer is simple, the governments can not close all bank accounts of all businesses and exchanges, because there will be always countries that will allow it for their own financial benefit. Despite of this, you have still the option to mine coins or buy them from other people directly.
Why would the government want to close the bank accounts of casinos since they make so much money off of casinos? Unless you're talking about illegal casinos that operate outside of government regulations and that might have their assets seized for operating illegally. Can't say I worry too terribly about those scenarios since they're operating outside of the law. It's not as if the government wouldn't grant a license if applied for, the more they grant the more tax revenue they rake in. The reason a casino wouldn't want to abide by such laws is most likely tax evasion, and unregulated casinos are also money laundering havens, so I'm not gonna lose any sleep over those rackets getting shut down.