Something about THC carts is killing people, while nicotine carts are not. In most of the states where people are dying, THC carts are a black-market item while nicotine carts are available legally. If legal nicotine carts are killing people, the business can be shut down and people held responsible. If black-market THC carts are killing people, the responsible party is not a legal entity that can be easily shut down.
Government inspections or not, anything you buy on the black market is inherently more risky than something sold legally through a legal entity.
Marijuana was 100% illegal for nearly a century, it's more legal now, yet the deaths are recent. I am very certain that there is some level of consumer bias toward buying supposed "underground lab" vaping products, having a higher amount of trust in them because marijuana is "legal" now. See where this might get confusing?