Opioid addiction

So I’ve been seeing the opioid addiction rate go up in my state. I just turned 18 July 20th and never have used hydrocodone or oxycodone but why are people addicted to pain pills? I take Tylenol PM every night to help me sleep so I’m pretty sure I’m apart of that opioid addiction rate! But mine is to help me sleep, what’s other people reasons? I’m just curious