Because your grandfather was told it made him healthier. And after a conditioning period, it kinda did. Then he felt like shit when he didn't smoke, kept smoking and felt better because of it.

Then he tells your dad he should smoke. Your dad might not like the idea, but enough grandfathers telling enough dads, eventually one picks up the habit. Now you see your friend is smoking, so you start too. The same thing happens to your dad. But then he sees new studies saying they cause cancer. Your grandpa did croak from lung disease. Maybe your dad should stop?

You get born. Your dad still smokes, but he tells you no. These things will kill ya. But your dad is your hero, and that cool kid down the road with the mullet and the black eye smokes too, and one day he offers you one. You take it, and try it. Gross. These things must kill you. Anything that foul must.

But then some of the richer kids start bringing these new things to school. They look like smokes, send puffs of smoke out, but smell and taste like cotton candy. These must be okay. Someone tells you they're even better than smokes, because they don't have the tar and nicotine. They just look cool and taste good. You pick it up.

One day, your mate offers you a puff from his vape and it makes your head swim. What was that? Nicotine, he says. It's not as bad as they say, he says. It makes him feel good, and its not as bad for you as cigerettes. You should try this mix. It'll make you feel great! So you do. You get a new vape to handle the mix.

One day, someone tells you that vapes will kill you as hard as cigerettes will. Popcorn lung? What's that? That's bullshit. They reckon you should take an edible instead. These aren't addictive, and aren't bad for you at all. If you pace yourself. These are strong. Take it easy. But you can handle it. Plus, these make you feel great! Surely something that makes you feel this good can't be bad for you.

And so on. And so on...