@jon Well, that bit I can explain. Shortly before the fall of the Wall, Frankfurt was "boomtown" of the DDR. That's why a lot of the street layout, the infrastructure seems to big. A city with shoes it cannot fill anymore.
I grew up as mostly a teen in the city throughout the 90s and sometimes I wonder if constantly feeling lost was brought upon by this mismatch.
But yeah. These places are quiet and empty most of the time. There certainly is no mass migration of foreigners there.
But it also fosters this feeling of being 'forgotten'. And by now, the city is not only too large in a way, but all the shiny new stuff from 30 years ago is now 30 years old and rarely gets renewed because there is no money.
Which leads to the weird effect that the failure of late stage capitalism is visible. Contrary to general belief, most places that look dilapidated in Frankfurt are the remnants of the early 90s.
I could rant about that town forever...sorry.