You don't understand, both comes from the same motivation and way of thinking: You see, compliance in Germany is about pretending to be super-compliant and not getting caught. Everyone will do the dance, make all the moves, and if you seem to make all the moves, you are assumed to be compliant. Supervisory authorities will not really check thoroughly except if you are annoying them or making them look bad. Especially if you are partially state-owned like VW.
In Dieselgate VW got caught, made the supervisory authorities and politicians look bad, which is why the authorities also weren't inclined to sweep it under the rug completely. They just shielded VW from the financial consequences in Germany (German VW customers got shafted).
Blocking GrapheneOS is the useless "pretending" part of compliance. They don't really want to do security, because that would cost money, so they pick some actions that seem drastic, harsh and don't cost them anything to implement. Later, when there is a security incident, they will point to their huge heap of pretend compliance, whine a bit about state sponsored actors, high criminal intent and other obvious deflecting bullshit. But they will get away with it, because they did the compliance dance, so they are obviously compliant and did nothing wrong. Nobody in authority will look twice als long as they are neither annoyed or made to look bad.
tl;dr: compliance in Germany is performative