Copypasta

It's lazy English.

I am.
You are.
He is.

Simplifies to:
I be.
You be.
He be.

It eliminates plurals.

SAE: Two dollars.
Ebonics: Two dollar.

It eliminates the word "the".
I am going to the store.
Becomes.
I be goin' to sto.

Basically, it's a lazy way of talking. It's also a form of aggression to show how little they care about the way they present themselves. If smelling like shit is offensive because it offends people nearby on account of poor hygiene, so too is using incorrect English a way of stinking up the intellectual area of people nearby.