Majority of them went there fully knowing they would be scammers. It is only 10% of them that probably thinking about working in casino or being a cook. Most of them just wanted to make money without thinking of the consequences.
Many years ago, most of these scammers were from Taiwan. Their Taiwanese bosses recruited people in Taiwan and sent them to sites all over the world to commit telecom scams. China cracked down on them hard. After awhile, they started operating in lawless places or places that don't have much of enforcement or can be corrupted and bought. Myanmar emerged as an ideal site for telecom scams. After a few years, locals and mainland Chinese started to take over the operation. By then, Myanmar became the biggest and most proliferate sites for telecom scams.
Most of these scammers are people that want to make fast money, seriously in debt, and young and unemployed that don't want hard labor jobs. Some of them just like those recent illegal immigrants that went to the US are already gotten in trouble for defaulting in China and tried to flee China.