[locallost]

Deutsche Bahn pays for the usage of the infrastructure just like any other company using it (e.g. Flix or any of the regional carriers). The infrastructure is the responsibility of DV InfraGO (formerly DB Netz).

[codemusings]

What are you talking about? DB Infrago is a subsidiary of DB and is as such governed by the board. The fact that they are separate entities has purely corporate legal reasons.

[locallost]

Deutsche Bahn still pays for the usage of the infrastructure and has nothing to do with maintaining it.

They are separate entities because it's mandated by the EU, the idea being it should promote competition in rail transport.