1. Support from the government.
Countries who gamble a lot has solid laws protecting their players so gamblers in those countries can just freely gamble as much as they want without having to worry about their rights. This doesn't mean that the countries have very free and loose rules but it just means that they have clear frameworks. Some other countries have some limitations but since their rules are clear, many still gamble.
2. Bigger paychecks.
Not all rich people are gamblers but they certainly have more chances to gamble if they wanted to. According to data, the higher the income is in some countries the more people gamble in that country. Since the average citizen is earning a lot, even if they spend quite a significant amount of money in gambling this will still not cause financial doom.
Is it fair to assume that a better economy and a solid framework will make people gamble more but be addicted less? This is the
source, by the way.
In my experience "bigger paychecks" is not necessarily true, as there are sites out there which accommodate for every currency or allow smaller denominations. Just look at poker rooms for a prime example, the lowest level many will go down to is $0.01/$0.02 blinds which allows people with even a couple dollars to potentially grind upwards. As a percentage of income, maybe that is a factor but at that point I'd also be looking at accessibility. Casinos probably make their most money from regulars, but if your internet/power goes down frequently or you need to work 12 hour days, then gambling can often be an after thought for the day - this breaks the cycle which generates the most profitable players for casinos.
To add to point 1, it becomes easier to track statistics if the players are allowed to gamble, but unless it's totally outlawed I'd imagine the amount of people who gamble in every country is roughly the same.