The answer is simple - there is no functioning city level garbage collection/disposal system. Outside of a handful of cities, there is no system to regularly collect garbage and dispose it properly. This is due to the sheer size and population of the cities combined with government and citizen apathy, lack of manpower, lack of funds, lack of knowledge etc.
> sheer size and population of the cities combined with government and citizen apathy, lack of manpower*,
This is something I see often. How come with a large population there is a shortage of manpower?
You see the same sort of thing in the UK, lots of people, high unemployment (more than twice what we have here in Norway), and yet there is a large amount of obvious work that needs doing like insulating houses and fixing holes in the road.
Lets see how it works generally in cities - millions of homes do their daily cleaning, there is no where to dump this garbage, so it is thrown street side or somewhere in a nearby small dump (https://scroll.in/article/802978/as-garbage-continues-to-pil...), then it is not collected for weeks, finally when it is collected it is thrown in a bigger dump (https://www.newsweek.com/trash-mountain-india-could-taller-t...). Only Indore that I know of (https://www.outlookindia.com/national/how-indore-became-the-...) is doing proper garbage collection and disposal.
p.s. my knowledge may not be fully up-to-date.