Starr and her father have a conversation about why so many young people are involved in selling drugs or gang activity. Why does this happen?

from the book The Hate U Give

The conversation between Starr and her father is a result of Khalil's death. Khalil was a childhood friend of Starr and she noticed that he was selling drugs, that was a common activity in Garden Heights. He justifies his activities alleging his grandmother lost her job at the hospital because she has cancer, and his mom is struggling to be clean, ironically, from drugs too.

Khalil dies from 3 gunshots in the back that came from one of the cops, he had the number 115 in his badge.