I have come to realize that laws such as this are driven by an unholy alliance between State Governments and Insurance companies who have a vested interest in minimizing damage claims.
The Insurance companies get the States to do their dirty work for them, but the State should not be in the business of imposing restrictions to people's freedom to protect the interests of a third party.
When seatbelt laws hit the books, I hated them and used every trick in the book to fool the LEO, even though I knew that every race car driver used a lot more seatbelt than in our cars.
After getting a $150 ticket, I started clicking. Gradually got used to the idea.
Not by intention you stated the most logical reason to use a seatbelt, “who have a vested interest in minimizing damage claims”.
I still don’t agree that they should fine you for not wearing one, but a better way might be if the insurance companies had a contract clause saying “if you are not wearing seatbelt and have an accident and have any injury, they don’t pay”. Sort of like if you leave your keys in your car and it gets stolen, they don’t pay.
Seems to me the insurance companies could simply include a clause in their policies stating they would not pay for injuries caused by not wearing a seat belt. Wait! That would eliminate the fines. Oh...