You cannot compare Thailand with Western countries for many reasons. When a country is not well developed, most people are poor, most jobs are simple, and education is basic or poor too, then most people have problems which makes them ignore "lesser" things like safety, environmental protection, and yes any kind of laws. For many a motorcycle is the only affordable family vehicle, and renting a taxi with seat belts simply out of question. Not unique to Thailand, and as long as the standard of living (for the poor people) does not improve these things will not and cannot change.