Not sure where you people live, but this myth has to stop, eventually. I can literally count on one hand the n. of shops NOT accepting cards - it's most of the times shops which, I guess, use cash to have flexibility in their accountings :)
The bigger mystery is why stores in some other countries are happy to have a payment method chosen by the customer eat into their profit.
But actually a lot don't, and when you try to pay, even contactless, with a non-Girocard, it won't work.
Visa and Mastercard don't magically let you on their network because you have a card machine.
In particular, I was staying in Nordhausen for work for a couple weeks. The hotel I stayed at tried to refuse to accept that I paid by card online in advance. Every small restaurant I went to refused to accept either a credit or debit card, and only a couple chain (read:overpriced) restaurants would accept Mastercard. When I tried to buy an Ethernet cable at a general store they refused to accept anything other than cash once they realized I was a foreigner.
Maybe it’s a myth in large population centres, but definitely not overall. I had roughly the same experience throughout most of Thuringia, with even gas stations in certain areas only accepting cash.