Certainly, as you said it's almost like everything is made to increase the profits of these centers' owners while limiting the earnings potential of Foreign teachers.
These guys are certainly not stupid, they know that we FTs don't need them, that we can find students in a blink and earn a lot more money on our own.
Think about it you know, most training centers out here charge 200 per lesson to students in large classes (30-40 students) and then pay 250-300 per lesson to the Foreign teacher.

As a self-employed Foreign teacher you can charge them 100 per lesson in classes of maximum 10 students. I let you calculate the earning potential.
It's a win-win situation for both the Foreign Teacher and the students.