Perhaps I'm misunderstanding but are you arguing that it's good restaurants evade taxes because it keeps their prices low?
Many restaurants (especially those with good service + good price) had to increase their prices a lot since then.
Sorry but what is a legit reason and it's a legit reason for what?
The EU also recently introduced and controls on credit card fees (that a merchant pays) with the aim of making it as cheap to transact as cash. That is of course only true if cash isn't being used to avoid taxation.
It fails if you want to buy food in the streets maybe, not every Doner can be paid by card.
But.. that's normal and aligns with what I see here in Singapore now: Cashless, unless small food shop/hawker place or something similar.
Germany doesn't accept _credit cards_ on a large scale. It does support paying with a card made of plastic usually..