This happens more often than you think. With us, a basic package for outdoor facilities (terrace, platform, parking space, access path, eaves strip, garbage bin area) was included in the house price, and I know at least 3 other large GUs that handle it similarly.
But it is not customary. Especially nowadays, the services of the GUs tend to decrease so that the price does not have to be increased.
Could it be that an architect/BU is obliged to ensure that the parking spaces expected by the development plan are also built? At least that they are applied for in the building application? I consider that plausible. When the builder ultimately implements something there is another matter.
At least in our case, the architect/GU applied for the carport at our request (the statics also have to be submitted), but the carport itself was built by the builder.
You can put a bicycle rack anywhere; I would neglect that as a GU, just remind the builder that it is necessary.
Otherwise, a GU does not have to do anything. You can accept or reject their offer. The latter would mean signing the contract with someone else.
Edit: A parking space must be approved, and that’s why the GU deals with it.
You plant a tree yourself; that is not approved ;)