Before opioid prohibition deaths from opioid use were quite rare. You ever heard a pothead drone on about "it's nearly impossible to overdose from smoking marijuana"? The same thing applies to smoking opium. It's nearly impossible to overdose on that. But prohibition has pushed us from opium smoking and oral laudanum to injectable heroin to fentanyl and now we're at carfentanil.
The current USian "opioid crisis" is another manifestation of opioid prohibition pushing people from safer, cheaper, less disruptive and deadly drugs to more deadlier ones. Two decades ago some USian opioid users could go to pill mills and get prescriptions for pharmaceutical grade opioids but the DEA kicked down doctor's doors a bunch and that ended up pushing people to the illicit market. Maybe next time you see those scary increasing graphs of opioid deaths vs time, give that a thought? Sum up all those deaths (compared to the baseline, prior to the increased LEA focus on "pill mills) and ask yourself: are all those needless deaths worth it?
For a unit volume (so, for a unit risk of ending up in a concrete box as a consequence of shipping/making raw product) of uncut/active material, you want to be able to sell the most diluted/cut doses to end-users. Of course people will want their chemist to synthesise carfentanil (over regular fentanyl), because you can supply the the same number of end-user doses with 10,000 times less active material. The harder the enforcement, the more potent this selection pressure gets: https://en.wikipedia.org/wiki/Iron_law_of_prohibition