Well.....demand is often ‘created’ by the suppliers... who are quick to change operations to suite the best means by which they can transport a drug and ease of, with the least risk.
Fentynal is about as easy as one can get....and very low risk of discovery.
The suppliers are the ones who introduce the latest drugs into the markets....and the addicts are always chasing the Dragon....so the cycle continues...as well as the blame game.
And the unchanging demand is for a high, not a chemical composition.