We are always quick to blame the illegal teachers, but at the end of the day, they aren’t the ones responsible for who the schools employ.
If schools can get away with employing anyone they want, there will always be people who will take the jobs they offer. The schools need to get into big trouble for employing someone who isn’t qualified, etc.
I heard about a guy who was reported for overstaying by his ex-girlfriend. Immigration went to his school and took him away. No caution or warning to the school. No checking of other teachers’ paperwork. Just in and out.
These are not international schools. These are language schools that have the word “international” in their business name.