TLDR: Vaporizer cartridges contain fillers. The fillers are apparently very expensive. The theory is people in the industry are trying to boost profits by using cheaper (never tested on humans) fillers that are potentially damaging to health. Whether or not this is true, I don't know, but it makes for an interesting theory.
https://news.ycombinator.com/item?id=20855683
TLDR: Vaporizer cartridges contain fillers. The fillers are apparently very expensive. The theory is people in the industry are trying to boost profits by using cheaper (never tested on humans) fillers that are potentially damaging to health. Whether or not this is true, I don't know, but it makes for an interesting theory.