The main reason is that the water pulls (dissolves) more of the plant material than you want. Said another way: The lower the proof of the alcohol (purity of the solvent), the lower the strength of the oil (% cannabinoids).So, if trichomes dissolve in alcohol in general, why the insistence on using only the very highest proof to make the oil? It would seem to me that most any alcohol would work. Is it that you need less of the higher proof ones and the lower proof ones have more water that needs to evaporate out so they are less efficient?
Why the focus on super high proof?