This is a good, but comprehensive (long!) interview with an economist Gordon T. Long, about why nations are devolving into a cash-free society. Basically, it gives them control of lots of pockets of money, like the cash in your pocket or the contents of pension funds. Nations are going broke, so they have to control every last bit of YOUR money.
Cash also prevents countries from going into negative interest rate territory. If people can use cash instead of paying banks to store their currency, then they would not use banks anymore–they would start using their mattress, or a safe at home. And negative currency rates are where some countries are now.
I recommend the first 20 minutes or so. If you really want to get into it, it lasts about an hour.