When you make gambling illegal you just drive it underground and fund organized crime, with all the additional crime and corruption that brings with it.
The arguments against making gambling illegal are similar to many of the arguments against making drugs and prostitution illegal, such as consenting adults should be free to do what they want as long as it doesn't harm anyone else.
So long minimum wage and workplace safety laws, welcome back indentured servitude.
In Korea, by law you have to prove you're a foreigner. In the Bahamas it is legal for the locals to bet, but the casinos kick them out. They've had enough experiences of a guy coming in on payday, losing his money, then his wife coming in the next day with a baseball bat to destroy the machine that took the money. Don't want any more.
That's almost certainly not the reason. They want the revenue but not the societal ills from gamblers.
Why should the government outlaw my ability to give my money away however I want to? If I want to go put all my money on black because it's fun to me, why should that be illegal?
There really is no reason to legalize gambling casinos. It is just an inefficient way of moving money around. It doesn’t actually create new value for society as a whole. (Friendly poker games amongst friends and family with small pots are probably fine).