Re "And yet their own intelligence agencies have no issue with sharing and working with the NSA."
The West German "intelligence agencies" grew out of ww2 - some where never vetted, some had their files lost or re written, some where invited in due to needed Soviet skills- no questions asked.
Over time they selected new staff, where exposed due to their ww2 crimes or retired. The next generation was guided into a world of expensive technology to help the NSA, CIA and GCHQ understand and shape the West German teclo system.
Great work, nice pay, dreamy budgets and on the winning team. This went on for decades and the West German staff got very comfortable ensuring the copper and later optical systems worked as installed by the USA. The GCHQ and NSA enjoyed full access to all aspects of West and later German telecommunications with the full help of tame, local German staff per site.
At some point other groups within the German gov would have had enough of all their communications, trade negotiations, science, politics just flowing to the UK, USA and a few other competing countries for free every day thanks to tame German gov and private sector staff.
At some point a white list of tame US and UK helping German staff with telco site/file access would have been created to ensure site access and pass/paper work.
Perhaps other groups in the wider German gov now have a short list of German telco experts/gov staff who are more loyal to the USA/UK than German.
Once the questioning starts beyond now 1 or 2 and grows to 10's, 100's will the US and UK offer their German helpers passports, pensions and residency outside Germany?
Like the nice interpreters get after other occupations are over.