Because, some event (getting hit by another driver, for example) you could be knock unconscious or be thrown from you
vehicle - then other in your vehicle could be seriously injured - and/or you driver-less vehicle could hit another vehicle.
Here in NY, they just announced enforcing seatbelts for rear seats. I agree with the point that they could trap you in a burning or crushed car. Lawmakers often never think of all sides of things; just as long as it sounds "safer". It has me wondering why this, now, with everything else going on. I've heard it suggested it's a way for the state to raise money through the $50 fines!.
If you assess 6
traffic points -- you will owe an additional 100 dollars per year for 3 years and for - each additional
point -add another 50 dollars per year for 3 years.
(in addition to any fine and surcharge)
This started back about the year 2005 or so.
I might be just a bit of - but ass we like to say - "Close enough for govt work"