For starters, I've confirmed your results for the United States using data from federalreserve.gov and alfred.stlouisfed.org:
If we take a look at the breakdown of bills in circulation, we can see that the value of $100 bill has drastically increased relative to the total value of bills in circulation but the others bills have not.
So people are indeed using cash less often for everyday purchases that most likely involve lower denomination bills. In short, people are most likely hoarding more cash in the form of higher denomination bills as a result of recent interest rate trends. According to a blog post by the St.Louis Fed, "the nominal interest rate on short-term bonds has declined essentially to zero, and, in this case, the best form of risk-free liquid asset is no longer the short-term government bonds, but money."
You might ask why people wouldn't just hold more money in electronic currency versus paper cash? If we compare paper cash to MZM (which includes various forms of electronic currency storage), we see that the % of the value in paper cash have actually gone down.
That said, if there was more confidence in technology and banking system, the % in paper cash could decline further. There also seems to be some arguments for a larger underground economy in the US since 2008. I couldn't find any long-term trends on financial literacy, but I also don't see how it would affect people to use paper cash over other forms of credit.