It's nothing other than the fact that they can do whatever they want to on a whim. The IO could be getting hungry and at that moment decide he want to make trouble for you. That is the fact. I don't care what visa you get on someone will eventually cause you trouble for whatever reason. They don't want you here Mr. Bigheart Farang coming to spread your benevolence and save the poor Thai people with your education, talent, or money. They just assume take your money, kick you out and laugh about it over a Chang.
Thailand is a dump, the people don't want you here. If you are wise you will already be preparing to get out while you still can.