Serious criminals who are on some kind of Interpol watchlist won't be able to travel to Thailand anymore, at least not by air. .
In the last few years, new systems were developed, including but not limited to APIS, SLTD & I-Checkit. Paired with biometrics and live checks of the Interpol database upon entry. Yes, there will always be ways, but the major holes have been plugged.
The schools simply don't want problem customers, especially if they have to issue a guarantee letter that is being used to vouch for the student at immigration. They also want to gauge if you actually intend to pay the bill and attend the class.
FWIW, if anyone doesn't want to use the class, I can gladly attend for you, eat, and learn more cooking.😆