I know...I was kinda joking. It's the synergistic effect of all the active compounds that produces the effect. Although I do think vapor thickness/amount is mostly correlated with overall potency/cannabinoid content, moisture content/RH and simply the quality of the grow/how well produced and apparent the trichomes and natural terpenes are. Lots of medical strains pass through my hands and I only ever smoke/vape 20% of them, I can tell from certain traits by nose and sight if it will produce vapor or give me a desirable effect. Main factor is trichomes to leaf ratio! Most pot in dispensaries these days is not grown to it's potential so that ratio is not usually up to par unless you know a skilled grower or are in a collective supplied by one.
Strains with best vapor content/thickest most expansive smoke seem to be indica dominant or Kush strains or strains with OG in the genetics(Afghanistan genetics), which is almost everything even though you can't tell unless you trace back and peel apart several generations of lineage and genetics. Indicas usually have physically much bigger trichomes as well, which might also effect vapor thickness.