Correct. Thais are notorious when it comes to overstaying and working illegally. Visa-free is granted after a risk assessment is done. In the case of Thailand it does not pass the test.
A relatively poor Thai will seize any opportunity to work for foreign cash to bring back home. I know quite a few in OZ who did this and bought a house or a small business back home. It doesn’t matter to them if they get caught, blacklisted and deported as the reward is worth it. So they’ll stay as long as possible.