The heightened use of $100 cash denominations should come of little surprise, as the article notes, "The number of outstanding C-notes has doubled since the financial crisis, according to the Fed. But it's probably not due to real demand to spend those large bills."
Basically, there is no established correlation between the rise of large-bill cash flows and legitimate economic activity, as demonstrated here:
U.S. $100 bills in circulation hit an all-time high last year, according to new data from the Federal Reserve out this week.Meanwhile, overall global demand for cash is slowing down.Some say the surge in $100 bills in the past decade may be a sign that global corruption is alive and well. These high-denomination bills tend to be the currency of choice for criminals because there’s no transaction record, and total anonymity.