The majority of these cases are not caused by synthetic cannabinoids, but instead the cutting agent used. This is why these cases aren't just isolated to THC/CBD vape carts, but nicotine vaping as well(if not more so).
There is a wide range of known cutting agents, and well known companies like
True Terpenes that make these cutting agents, as well as a wide range of lesser known cutting agents like
Honey Cut, and it appears as though many of these companies aren't being honest about what they are using, as you will see if you follow the links provided.
Many might say "well what an evil thing to do" or "how could this be legal", well, pure THC distillate is near solid at room temperature, and CBD will start to crystalize at concentrations above 60% or something around there. So there are honest uses for these types of products, however, there is a lot of dishonesty in not only the application(people using cutting agents to increase profit/product amount), as well as a lot of dishonest manufactures. So while, yes, it is possible to put synthetic cannabinoids into a substance that appears similar to THC/CBD distillate, it's going to be much more likely that the manufacturer that made the carts is receiving the distillate 2nd or 3rd+ hand from the source, each likely adding 10-20% cutting agent, then it is put into cheap knock off carts of the most popular brands. So it looks as if there are only 100s of cart manufacturers when really there are 100s of 1000's.
And while yes, you're likely inhaling pesticides and heavy metals from a black market cart, it's highly unlikely that these would be in high enough concentration to cause lung damage. The lung damage is likely caused by accumulation of various cutting agents in the lung, causing lipid pneumonia or another type of lung disease. The pulmonary embolism is probably from extremely high levels of nicotine that is commonly consumed by nicotine vapers who mod their vapes and try to blow the biggest clouds. Or a combination.