German implementer here. We have to use some kind of attestation mechanism per the eIDAS implementing acts. That doesn't work without operating system support. The initial limitation to Google/Android is not great, we know that, and we have support for other OSs on our list (like, e.g., GrapheneOS). It is simply a matter of where we focus our energy at the moment, not that we don't see the issues.
German citizen here. So why is an implementation going forward when you already know it will not serve all citizens? Why are we not refusing to implement this until we know we can make it work on all devices? Personally I recently switched from an AOSP based android without Google Play to Ubuntu Touch. In the future with better hardware support I will probably switch to postmarketOS.
If you were averse to carrots (without any health restrictions on eating them), would every government institution in Germany be required to serve you carrot-free food?
If not, why should they be forced to accommodate every smartphone brand in existence, even if there's only 3 people in Germany using it? THe list has to end somewhere.