China is still a relatively poor country (1). I lived in Shanghai for a few years back, and even if you just go into the side streets a few blocks from the richest area in Shanghai (Pudong, Huangpu), you can see slums and sometimes dead people lying in the streets with no assistance. And if you go 10 minutes out of the richest areas, you have people living in hutongs and communist-style buildings with low level life qualities.

The problem is that these immigrants will never be able to become a first-tier city citizen, due to hukou. The government is trying to move these people into empty buildings in second tiered cities, but there are no jobs there. (thus alot of these migrants actually moved back to the farms last I heard)

1.) Statistica says that in 2016, China rural households only made about $1000/year. and urban households only made about $3000/year. (https://www.statista.com/statistics/259451/annual-per-capita...)