Because we had (and still do have) an epidemic of fatal abuse of labeled, regulated opioids. I'm not saying restriction works either; I'm rejecting the pat solutionism of the original comment and acknowledging how difficult the problem is. Maybe legalization is a good idea, maybe not; what it certainly isn't is a solution to opioid deaths.
And I believe the problem isn't so much that those legal opioids are dangerous, because in theory you still have a medical system to curb access. It is that they are addictive, and that users who get addicted will either abuse them or switch to illegal drugs if they can't access them.
I am not against drug legalisation, on libertarian grounds. If you want to kill yourself, kill yourself, it's your life not mine. But I don't buy that banning drugs results in more harm that making them freely available.
And it's very paradoxical for liberal societies to want to ban or heavily control the use of alcohol and cigarettes and to consider legalising hard drugs at the same time.
I'm not advocating for legalization. I'm pushing back on what I felt was a too-pat appeal to legalization and labeling as a cure-all for opioid deaths.