Why are so many South Africans teaching English in Asia?

I am in Korea atm and noticed the most common origin of English teachers here is South Africa. I never met so many South Africans before. These South Africans generally don't have a lot of money, are white (some Indian but haven't met any blacks), and are older than other English teachers.

Some of them weren't able to get visas and are working here informally. One ~40yo lady I met is so introverted it must be painful for her to teach in front of a class. And I heard from friends the situation is similar in other Asian countries. There are so many South Africans they are driving down the market salary for teaching English.

Do South Africans not have a better choice than teaching English in Asia?