You can' just generalise that if one place can work without seatbelt laws, all places can. There are many factors to consider including cultural differences, population density and size, education and climate. What may work somewhere else may not work here. It may be that laws are created because the alternative is not working, even if it works in other places. As an example, throwing up in a taxi incurs an instant €80 fine in Ireland. This law is not necessary in most other countries because it is not a regular occurrence there.
Regarding buses. They have trained and vetted drivers that are watched over much more extensively. Additionally, due to the size of buses, most collisions with other cars would have much larger effects on the other vehicles than the bus. They require much more turnover of people sitting in a certain location, drive at lower speeds, and remain within their designated paths.