They bring the property value down. They can buy the land at a lower price. Then they move all the people out, raise the property value and sell it at a profit.
11 seconds sound clip from the Boyz n the Hood movie soundboard.
You can hear this line at 01:04:41 in the Blu-ray version of the movie.
Quote context
[...]
- What are y'all, Amos and Andy? Are you Steppin' and he's Fetchit?
- I'm talking about the message. What it stands for.
- Now, what we need to do is we need to keep everything in our neighborhood, everything, black.
- Black-owned with black money.
- Just like the Jews, the Italians, the Mexicans and the Koreans do.
[...]