The point of a directive is that it outlines what kind of law should be written in each member state, but each member state has a lot of leeway regarding how they decide to implement the directive.

Then there are another category of EU laws: Regulations. Regulations must be precisely the same in each member state.
But, if what you say is true and it's indeed in a directive instead of a regulation, then the reason is simply that Germany decided to implement the directive in a way that doesn't require ATMs to give receipts.

A directive defines the rough outlines of a law, a regulation is a ready-to-use law that cannot be altered in any manner whatsoever and is automatically valid without parliamentary interference by the member states.