TLDR: Different kinds of wheat in the flour (softer, with less gluten). The soft wheat flour is sort of hard to get if you aren't a commercial baker, but you can get it on Amazon, although it's $10 instead of $2.50 like regular flour.
biscuit cake flour
Seems plausible.
TLDR: you must use a soft wheat flour such as White Lily, Martha White, or Southern Biscuit. Here's a URL where they make/show biscuits made with all 3 brands:
https://www.wired.com/2012/05/best-biscuit-flour/
TLDRSQUARED: Order of best taste: Southern Biscuit flour, Martha White flour, and White Lily flour (last).
What's arbitrary about it?
Judgment of food ingredients should be based upon taste, flavor, texture and appearance of the results rather than upon the number of Google results, say. Now _that_ would be "arbitrary".