It's not a secret nor hidden. It's well known and something people want to avoid. Users don't intentionally take a dose dozens of times higher than helpful.
Blaming it on fentanyl is a red herring. The real issue is mislabeling. If people sold heroin instead of codeine or Tylenol, we'd see the same problem.
Huh? That's the exact drug that killed the person in the story. It's made quite clear:
Lucas County chief toxicologist Robert Forney and his staff meticulously screened DJ’s blood for drugs. Forney’s team didn’t find any heroin.
What they did discover was a lethal dose of fentanyl.