Earlier quoted context omitted.
That's just not true. People pay by cash all the time in Denmark. I happened to read this in line at a Danish supermarket and people were paying with cash as much as with cards while I was paying attention.
Visited Denmark twice in 2015 and I can testify that using cash was perfectly normal.
Since then, to July 2015, there's been a 25% increase in card payments, but only a 12% increase in total value [2], so smaller things must be being paid for by card.
Contactless cards were only introduced in Denmark in 2015, and payment by mobile phone in 2013 [3].
So yes, it's normal. But it's not the most common form of payment, and I've been asked by a guy selling sausages from a wagon to use a card when I offered cash.
[1] http://www.cfir.dk/Arrangementer/andrecfirarrangementer/frem...
[2] https://www.nationalbanken.dk/en/bankingandpayments/danish_p...
[3] http://www.mobilepay.dk/da-dk/pages/The-story-in-English.asp...