Because proper low temp dabbing relies on the
Leidenfrost Effect
Too low of a temp will actually
burn the oil since it lends to suboptimal conditions regarding creating the LE. Basically it's hot enough to burn the oil but not hot enough to create that insular barrier of vapor.
Of course if you go low enough you won't burn the oil, but at the same time you won't produce any significant quantity of vapor in any reasonable amount of time.
Case in point, on my first test run for that video I had the voltage at 7.4v which was too low. My dab sat in that glass bowl for literally two minutes, as it slowly boiled off, releasing very unsatisfying amounts of vapor. *It was basically a huge waste of time and oil.
*edit: this actually may be beneficial regarding seasoning the quartz when it's new.
@THC SCIENTIFIC if you notice that vapor/smoke you are talking about is at the end of the dab, after a majority of the mass has vaped off and I was no longer inhaling, thus drawing cool air over the nail. I had burnt residue in the bowl after that dab, but only because there was a small amount of oil left over which sat on the nail and cooked to death after my initial hit.