Because there is no 'regulation' yet, homebrewers are making the vaping liquids and selling them to smoke shops, etc. They use dangerous chemicals because they are cheaper.
It is possible that the homebrewers make the THC products, but I doubt it. They can't legally sell those in most states. In any case, it needs to be regulated.
Uhhhh, illegally made THC cartridges appear to be as popular in States where weed is illegal as the weed itself is...
I know, who would have think that folks already selling an illegal product would figure out other ways to sell that illegal product? Gobsmacked here, I tell you, Gobsmacked...