As a German I find it interesting that foreigners think that this is a cultural thing.

It is not. It's the law.

In Germany you are not allowed to photograph people without their written and signed consent. Any conference or event counts as a private event when it is organized on private property. If it's not a building or space owned by the city, it is private property. This includes e.g. swimming pools owned by the Stadtwerke (there have been lawsuits because of that, all decisions in favor of privacy).

For example, even cameras that protect your property by filming the outside area are not permitted to film the street, and they have to be arranged to point towards your own property. That's why even banks have cameras always on the corners of the building, pointing back to their own property.

Again, it's the law. It's pretty strict about this sort of thing, especially because of WW2 and post WW2 times, where a lot of people died because of Stasi misinformation or Zerstörungstaktik related things.

Source: was a helper and organizer of a lot of CCC events before 2021.

GDPR/DSGVO means you have to get written consent by all visitors, otherwise you cannot make photos of the event and publish them.