Because people this stupid never used to survive to adulthood. Advances in medical sciences + a much more risk conscience/risk adverse society have permitted people like this to survive well past the years that nature would have allowed of her own accord.
I'm fascinated with stupid people and the stupid things they do. It's a guilty pleasure.
Some people are interested in science or space, others like to study history or finance.
But for me, it's dumb people.
When I see a dummy like the guy in the video, I don't even relate to him as a human. He's like an exotic animal or even a space alien to me. I know, it's terrible.
Endlessly fascinating.
That plus another thing which has been expurgated from our society: humiliation. In the past, let's posit that this guy may - *may* have survived, minus a hand. For the rest of his life, he would have served as a warning to others, and been a walking, teachable object to youngsters. "Looky there! You see that guy? He lost his hand - you know why? Cuz' he was STOOPID enough to play with a rattler! You wanna lose yer hand, boy?" If that were attempted today, the parent would be sued for disrespecting the disabled.