why does Amos think taht black people are"too envious of one 'mother"

The quote is:

"Us colored folks is too envious of one ‘nother. Dat’s how come us don’t git o further than us do. Us talks about de white man keepin’ us down! Shucks! He don’t have tuh. Us keeps our own selves down."

Amos is referring to how black men seek to limit each other's success. They are jealous and envious when another black man gets ahead.