Hard to make money when you kill off your customers. Most of the fentanyl being smuggled into the US comes from China, though. Regardless, this is still good news.
Search Engine’s “Why are drug dealers putting fentanyl in everything?” podcast episodes go pretty far into why it’s happening despite it killing customers. It’s pretty good.
There is a ton of info over two episodes, like they even visit one of the Chinese laboratories under the guise of being a potential customer, really worth going through the whole thing.
On the specific topic, it’s cheap and differentiates the product. Someone who buys it will get a different (better?) high than they can kind anywhere else, and they’re more likely to come back for more. It can also be added to substandard product to make it seem “better”. It’s not a long lasting effect either, so people will want more sooner.