They were in just any district.
Pidgeon keeping is a real thing, for sports (pidgeon races), just admiring them (as pets), for food, as messenger pidgeons...
I can offer one other possible explanation besides squab. Manure.
According to this site on Micro-livestock:
Pigeons are traditionally raised in dovecotes - "houses" that protect the birds from the elements and from predators. This system allows free-ranging flight and requires almost no human intervention. Dovecotes are a good source of both squab and garden manure, and they continue to be used, especially in Egypt
The buildings you show seem to match the dovecote, specifically the 'urban' design. So if they weren't harvesting the pigeon, it may have been a convenient method of obtaining hard to get, free fertilizer in city areas for gardens.
Pigeon keeping was widespread in Russia (and perhaps some other countries of future USSR) even before the Soviet Union. The birds were kept as purely decorative pets, with no practical use whatsoever. They were not, under normal circumstances, eaten (except at times of famine), not used as messenger birds (there were messenger pigeons, but they were raised at more specialized facilities). Mostly, wealthy enough villagers would spend money on buying exotic pigeons to keep in their pigeon houses. "Exotic" not only in terms of appearance but also in terms of their flying pattern. There were some techniques to control their flight from the ground, to a degree - like waving flags or something. Dedicated pigeon keepers would brag for hours who has better pigeons and how they fly, etc. To my knowledge, the tradition declined later in the Soviet Union, but was (or is) still present.