Just about anybody can set that kind of thing up by themselves. Whether teaching English or Chinese, why interview with an employer, when you can set it all up, work remotely, independently and keep all the profit?

Besides, those types of online employers have a reputation for not paying. It's that little bit more difficult to find somebody who ripped you off and kick their head in/sue them, when you've got to fly somewhere else and can't be exactly sure where they are based. At least, if you're employed at the school, you know where to find them and deal with matters.