This is because they're taking very large quantities of opioids and suffering the side effects, and they've developed a tolerance so they need larger more risky doses, and because it's probably not treating the problem they started taking opioids for.
And yes, by idiot thrill seekers, and people carelessly combining their opioids with other drugs (e.g., zolpidem) or alcohol. But that's a minor issue, in the context of the pain relief that they get.
I do admit, though, that US doctors have tended in recent years to over-prescribe. Partly because it's faster and less hassle to prescribe opioids than physical therapy. And because physical therapy tends to cost more for patients and insurance companies. And also because the compliance rate for physical therapy tends to be low. People are busy, and want quick results.
But still, focusing on addiction as the main problem is, in my opinion, misguided. It's better to focus on people being well, and able to enjoy their lives. And if, for whatever reason, that means taking opioids until they die, that's just how it is.
That's mostly because the drug they're addicted to can't readily be purchased. So they're stuck buying stuff illegally. Stuff that's expensive. And with unknown potency. Or even, for that matter, identity.