The city doesn't want it, the federal government is pushing for it. Probably because the person in charge is a free market theologist from FDP so he wants to spend as much tax money as possible to have as little impact as possible. Wait, that doesn't make a lot of sense, but it's what's happening.
Instead they could build it a couple kilometers further out to still connect the ring, the distance in drive time would probably be less than 5 minutes.
But they stick to stupid plans they made 10 years ago like they always do in this city.