In addition to all the things you mentioned, I also blame a certain amount of the problem to the child being in the back seat and often asleep and quiet.
Like you, I am grateful that no serious harm befell during the “growing years”. The guilt would be unbearable.
That's it. Out of sight, out of mind.
Unintended consequences of requiring the children to be in the back seat.
My car, and many others have clear windshield and front side windows. The rear sides and rear are heavily tinted, from the factory.
Child asleep in the car seat, mom/dad been driving some time, in a rush. He/she gets out of the car, glances around but can't see in the drivers side rear window. Doesn't see the baby.
Mom needs to place her purse or something she can't do without in the back seat next to the car seat. What could father use?