[TomK32]

Because passports are the international standard, issued under international guidelines while identity cards aren't.

[hocuspocus]

The international standard is completely irrelevant here. The parent poster specifically mentioned the case of EU citizens.

As a EU citizen you can settle in Germany without owning a passport. It's not up to private companies to redefine what consists in a recognized official form of identification.

[germanier]

EU national identity cards are issues under EU guidelines and recognized by the authorities of all member states.