"But producers also had another incentive to lower the alcohol content of a spirit—a motivation that has arguably had a greater influence on why spirits today are often weaker than spirits of 50 and 100 years ago: money.
Simply put, more dilute spirits are cheaper to produce. Not only does doing so allow distillers to get more bottles out of every drop of alcohol they produce (a drop in proof from 100 to 80 can create about a half-dozen extra cases per whiskey barrel for a distiller), but each of those bottles carries a lower tax burden, which, in the U.S., makes the federal taxes on an 80 proof bottle 53 cents lower than on a 100 proof one."
That part of the equation was pretty clear, ever since the dustup with Maker's Mark a couple of years back. I didn't really know where 80 came in as the baseline however. And speaking of unusual ABVs, I was gifted a bottle of Mount Gay Eclipse overproof recently - bottled at 154 proof, or 77% ABV. I wonder if 154 is the "normal" overproof number in Barbados (the origin of the bottle I believe)?