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.
Gambling is a big source of revenue and employment for countries and that is why they do their best to ensure that it is a very highly regulated industry. If they don't do that the money that is supposed to go into the covers of the government would be lost and that would be bad for the economic growth of the government of such a country. In terms of the employment it offers, many people get employed and paid and the money ends up getting into circulation in the economy.