Not an expert on the topic, but IIRC this is the rough outline:
- The main ISP of Germany is Deutsche Telekom, a formerly state-owned company that was privatized ~25 years ago, which Germany still holds stock in
- In the past Telekom was awarded big contracts to expand broadband access across the country
- Telekom is/was really slow at fulfilling those contracts, and at the same time behaves in an anti-competitive manner towards any independent ISPs that try to fill the void
- The government doesn't punish any of that behaviour like they rarely do with a big German company, even more so with privatized ones that they have a stake in
To also be fair towards Telekom a bit, Germany is a very decentralized country, which is a boon in a lot of situations, but also challenging for any infrastructure projects. Part of the contracts was that they also have to expand broadband access in all rural parts of Germany.