Actually the trend is the opposite.

Schools have dropped their requirement of native speakers in many cases and are now recruiting non-native speakers from Europe and the Philippines.

Regarding the practical necessity of the TEFL, a person who knows the language can gain a lot of teaching methodology by teaching practice, as well as from the in-house training that schools themselves provide.

I am not sure the TEFL is necessary but I think schools require it hoping that the TEFL schools would weed out bad speakers for them, since the school owners could not themselves tell if the applicant's English were perfect or not.

One's ability to speak and know good English depends on how the parents spoke at home, although it is possible to learn that at school. But it is secondary, not tertiary, that determines the level of English spoken.

There is nothing morally wrong with having a fake TEFL but someone would be foolish to brag about it. (Neither William Faulkner nor Bob Dylan nor Shakespeare had a college degree.)

The TEFL should be used simply as an administrative tool: some government bureaucrats need to check off that box on a form. Having a TEFL does not mean the holder is not trash, and having a fake one does not mean the holder is.