This is a perfect example of globalization and urbanization and overpopulation fucking the lowest classes over. Because urban space everywhere is taken up by the urban upper class, the only places informal marketplaces can operate and compete for a piece of the pie are where the urban upper classes and the foreign upper class tourists intersect with the public transit system. In this case, literally inside the most precarious spots — the train tracks themselves.
A relevant, and more recent, term from the Marxist glossary:
The law of uneven development states that once a world market has engulfed all countries in the world and comes under the domination of finance capital, the road of capitalist development, followed in the past by the old capitalist powers, is blocked for newcomers. The wealth and power of the great powers is maintained only by the exploitation and impoverishment of the colonies. In their search for sources of cheap labour and raw materials, the imperialist powers distort and stunt the development of culture in the colonies. These colonies do not simply “lag behind”, but rather their development is the “other side of the coin” of the advanced conditions enjoyed in the great powers.