They are capable aircraft and cheaper than American fighters both in price and maintenance, these days nobody wants to rely on America, besides which... who is going to attack Thailand, it's another waste of money like the submarine.
You think that's easy? That was a revolutionary idea, stepping out of the box so to speak, making a wheel and axle was another difficult step to master. wheeled vehicles are no use without rudimentary roads, they aren't much use in jungles.
Corruption is everywhere, it's just better hidden in the West because there are consequences (unless you are the mayor of NYC protected by a corrupt president)