How many terrible teachers are allowed to continue to teach after decades of disastrous results?
How many ideologues with no interest in teaching, but every interest in indoctrinating young minds, are tolerated because the alternative is "no teacher" and the class wouldn't run?
How many teachers who would fail state exams, teach, despite relying on answer sheets to be "competent"?
I agree with you that on the top end of education, this is no replacement and at best a supplementary tool. For the poor kid in a bad neighbourhood whose teacher is more interested in "de-colonizing" mathematics than teaching mathematics, this is a Godsend.