The point is that the merchants have decided not to support MC/Visa, because of the higher costs. And this now slowly changes after the EU regulation for merchant fees is in place. All terminals that support Girocard are Chip/PIN terminals (Girocard is a Chip/PIN only standard) so there is no limitation here in the installed POS terminal base.
Three things: the merchant fees for debit cards are max. 0.2% now. But that is not what big department stores and grocery stores like Aldi are paying. They negotiate the merchant fees differently and end up with much lower fees for Girocard acceptance. They don’t pay much at all. It is true that Girocard is a little bit behind in technology in some points (live notifications), but that is about it. Girocard is now also contactless and can also virtually run on a smartphone and it is a perfectly running and very reliable system.
Second: the electronic direct debit system. This is not part of the Girocard brand. But the data encoded on Girocard branded bank cards is used to transmit bank account details to a merchant who then can withdraw the amount for a one time payment as a SEPA direct debit transaction. This is even cheaper for merchants, yet more risky, because customers can return the payment like with any SEPA direct debit. Sometimes you end up with a merchant that only offers this option and then even Maestro cards are not accepted.
And third: Germans like to pay with cash. Its weird. I don’t get it. But its a fact that a majority of customers still prefers this.
It is not just about old vs. new here. It is about different players and standards in a market that compete with each other. And since Girocard is by far the one with the biggest market share here, it is not going anywhere very soon.
To be clear, I am not a fan of the Girocard system. The irony is that its wide adoption and good performance makes it hard for competing players here to gain market share. And the banks who could focus on selling their customers MC/Visa debit cards with slightly more functionality, have little to no interest because they are the ones running the Girocard system.