In too many cases, it's merely a business, and not a form of education. This has led to an industry where at least half of the teachers (in my experience) have no interest in teaching, they merely use it as a means to live in Japan.
Eikaiwa is partially to blame, but I'd lay the most blame on the government for having no standard in their ALT system. Properly, it would require some certification to teach, and the government would be willing to subsidize TEFL training for any foreigner being hired as a teacher. Instead, they just contract the work out to the lowest bidder, without any interest in those companies' training.
There are lots of good teachers and people passionate about teaching, but it's usually in spite of the system, not because of it.