Mostly it is because it is young, higher proof, run hard, or into the heads and/or tails.
The process is pretty easy and the equipment isn’t as critical as the marketing material claims but adjuncts to matter a lot.
If “purity” was the best Skyy vodka would be considered the best in the world as the use RO for water and get train cars of commercial ethanol shipped in.
I did a lot of work on starting a distillery before one of my business partners flaked out and the venture failed but there are only 4 things in any booze.
Water, ethanol, flavorings, and bullshit.
Grey Goose as an example, which is considered an upmarket vodka is mostly smooth because they skate the legal line for “adjuncts” to make it smoother.
In rectified spirits like vodka, especially vodka like Skyy which is typically distilled in 90+ plate stills there isn’t many fusel oils like butanol, isoamyl isobutyl, or n-propyl but there will be more in any other spirit that isn’t as pure like any whiskey.
But most of the serious flavorings really require attempts to *add *like:
smoky: guaiacol, 4-ethylguaiacol, 4-vinylguaiacol
sweet smoke: syringol and syringaldehyde
clove: eugenol, isoeugenol
Funding and scale size for barrel storage is the main blocker for aged liquors, but in the case of white spirits like white lightning or vodka it is more about energy consumption and hiding the acrid true pure alcohol flavor.
Economics, production velocity and marketing are a large portion of this, and while the information is proprietary, *moonshine * as a “product type” and not a description of non-tax paid spirits is just unflavored, unaged whiskey or rum.
Consistency is the hardest part obviously, but as the BS (aka marketing) in the industry is the rule and not the exception here is a book that will reliably go over the implications and causes of flavors.
The Alcohol Textbook: A Reference for the Beverage, Fuel and Industrial Alcohol Industries
They big boys have nothing over the simplest moonshiner setup even one using pressure cookers and copper pot scrubbers for unaged pot still booze.